diff --git a/fmt/fmt_8long.c b/fmt/fmt_8long.c
index 7a372f6..f44c242 100644
--- a/fmt/fmt_8long.c
+++ b/fmt/fmt_8long.c
@@ -19,5 +19,7 @@ size_t fmt_8long(char *dest,unsigned long i) {
 int main() {
   char buf[100];
   assert(fmt_8long(buf,012345)==5 && !memcmp(buf,"12345",5));
+  assert(fmt_8long(buf,0)==1 && !memcmp(buf,"0",1));
+  return 0;
 }
 #endif
diff --git a/fmt/fmt_8longlong.c b/fmt/fmt_8longlong.c
index 97cb9bf..f2638c8 100644
--- a/fmt/fmt_8longlong.c
+++ b/fmt/fmt_8longlong.c
@@ -19,6 +19,8 @@ size_t fmt_8longlong(char *dest,unsigned long long i) {
 
 int main() {
   char buf[100];
+  assert(fmt_8longlong(buf,0)==1 && !memcmp(buf,"0",1));
   assert(fmt_8longlong(buf,0123456701234567)==15 && !memcmp(buf,"123456701234567",15));
+  return 0;
 }
 #endif
diff --git a/fmt/fmt_escapecharc.c b/fmt/fmt_escapecharc.c
index 47eb5e1..99fb779 100644
--- a/fmt/fmt_escapecharc.c
+++ b/fmt/fmt_escapecharc.c
@@ -80,6 +80,7 @@ int main() {
   assert(fmt_escapecharc(buf,'1')==4 && !memcmp(buf,"\\001",2));
   assert(fmt_escapecharc(buf,0xfefe)==6 && !memcmp(buf,"\\ufefe",6));
   assert(fmt_escapecharc(buf,0xfefec0de)==10 && !memcmp(buf,"\\Ufefec0de",10));
+  return 0;
 }
 
 #endif
diff --git a/fmt/fmt_escapecharhtml.c b/fmt/fmt_escapecharhtml.c
index 23e5699..f39345e 100644
--- a/fmt/fmt_escapecharhtml.c
+++ b/fmt/fmt_escapecharhtml.c
@@ -6,4 +6,6 @@ size_t fmt_escapecharhtml(char* dest,uint32_t ch) {
   return fmt_escapecharxml(dest,ch);
 }
 
+/* unit tested via fmt_escapecharxml.c */
+
 #endif
diff --git a/fmt/fmt_escapecharjson.c b/fmt/fmt_escapecharjson.c
index 7a39ef0..b943f89 100644
--- a/fmt/fmt_escapecharjson.c
+++ b/fmt/fmt_escapecharjson.c
@@ -1,5 +1,11 @@
 #include "fmt.h"
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "fmt_tohex.c"
+#define UNITTEST
+#endif
+
 static void fmt_hex4(char* dest,uint16_t w) {
   dest[3]=fmt_tohex(w&0xf); w>>=4;
   dest[2]=fmt_tohex(w&0xf); w>>=4;
@@ -45,3 +51,21 @@ simple:
   }
   return n+6;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+#include <string.h>
+
+int main() {
+  char buf[100];
+  assert(fmt_escapecharjson(buf,'f')==6 && !memcmp(buf,"\\u0066",6));
+  assert(fmt_escapecharjson(buf,'\b')==2 && !memcmp(buf,"\\b",2));
+  assert(fmt_escapecharjson(buf,'\n')==2 && !memcmp(buf,"\\n",2));
+  assert(fmt_escapecharjson(buf,'\r')==2 && !memcmp(buf,"\\r",2));
+  assert(fmt_escapecharjson(buf,'"')==2 && !memcmp(buf,"\\\"",2));
+  assert(fmt_escapecharjson(buf,'\\')==2 && !memcmp(buf,"\\\\",2));
+  assert(fmt_escapecharjson(buf,'/')==2 && !memcmp(buf,"\\/",2));	/* I'm baffled as well */
+  assert(fmt_escapecharjson(buf,0x1d11e)==12 && !memcmp(buf,"\\ud834\\udd1e",12));	/* utf-16 surrogate pairs */
+  return 0;
+}
+#endif
diff --git a/fmt/fmt_escapecharquotedprintable.c b/fmt/fmt_escapecharquotedprintable.c
index 2b07170..790275d 100644
--- a/fmt/fmt_escapecharquotedprintable.c
+++ b/fmt/fmt_escapecharquotedprintable.c
@@ -1,5 +1,11 @@
 #include "fmt.h"
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "fmt_tohex.c"
+#define UNITTEST
+#endif
+
 size_t fmt_escapecharquotedprintable(char* dest,uint32_t ch) {
   if (ch>0xff) return 0;
   if (dest) {
@@ -9,3 +15,13 @@ size_t fmt_escapecharquotedprintable(char* dest,uint32_t ch) {
   }
   return 3;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+#include <string.h>
+
+int main() {
+  char buf[100];
+  assert(fmt_escapecharquotedprintable(buf,'f')==3 && !memcmp(buf,"=66",3));
+}
+#endif
diff --git a/fmt/fmt_ulong.c b/fmt/fmt_ulong.c
index 7b7bc4a..ea123b3 100644
--- a/fmt/fmt_ulong.c
+++ b/fmt/fmt_ulong.c
@@ -17,5 +17,6 @@ size_t fmt_ulong(char *dest,unsigned long i) {
 int main() {
   char buf[100];
   assert(fmt_ulong(buf,12345)==5 && !memcmp(buf,"12345",5));
+  return 0;
 }
 #endif
diff --git a/fmt/fmt_utf8.c b/fmt/fmt_utf8.c
index 9e26eb7..de2202d 100644
--- a/fmt/fmt_utf8.c
+++ b/fmt/fmt_utf8.c
@@ -25,3 +25,4 @@ size_t fmt_utf8(char *dest,uint32_t n) {
   return 0;
 }
 
+/* unit tested via scan/scan_utf8.c */
diff --git a/fmt/fmt_xlong.c b/fmt/fmt_xlong.c
index 37a66f8..06c4654 100644
--- a/fmt/fmt_xlong.c
+++ b/fmt/fmt_xlong.c
@@ -24,5 +24,6 @@ size_t fmt_xlong(char *dest,unsigned long i) {
 int main() {
   char buf[100];
   assert(fmt_xlong(buf,0x12345)==5 && !memcmp(buf,"12345",5));
+  return 0;
 }
 #endif
diff --git a/mult/imult16.c b/mult/imult16.c
index 13d86f4..06cb797 100644
--- a/mult/imult16.c
+++ b/mult/imult16.c
@@ -16,3 +16,16 @@ int imult16(int16 a,int16 b,int16* c) {
 }
 
 #endif
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  int16 a;
+  assert(imult16(4,10000,&a)==0);
+  assert(imult16(-4,10000,&a)==0);
+  assert(imult16(5,10,&a)==1 && a==50);
+  assert(imult16(-3,10000,&a)==1 && a==-30000);
+  return 0;
+}
+#endif
diff --git a/mult/imult32.c b/mult/imult32.c
index 1073490..40e5b94 100644
--- a/mult/imult32.c
+++ b/mult/imult32.c
@@ -16,3 +16,16 @@ int imult32(int32 a,int32 b,int32* c) {
 }
 
 #endif
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  int32 b;
+
+  assert(imult32(0x40000000,2,&b)==0);
+  assert(imult32(-0x40000000,2,&b)==1 && b==-0x80000000ll);
+  assert(imult32(0x3fffffff,2,&b)==1 && b==0x7ffffffe);
+  return 0;
+}
+#endif
diff --git a/mult/imult64.c b/mult/imult64.c
index 79f2f7b..0cb06e7 100644
--- a/mult/imult64.c
+++ b/mult/imult64.c
@@ -32,3 +32,18 @@ int imult64(int64 a,int64 b,int64* c) {
 #endif
 
 #endif
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  int64 c;
+
+  assert(imult64(0x4000000000000000ll,2,&c)==0);
+  assert(imult64(-0x4000000000000000ll,2,&c)==1 && c==(int64)-0x8000000000000000ll);
+  assert(imult64(0x3fffffffffffffffll,2,&c)==1 && c==0x7ffffffffffffffell);
+
+  return 0;
+}
+
+#endif
diff --git a/mult/umult16.c b/mult/umult16.c
index eba66dd..9bc0170 100644
--- a/mult/umult16.c
+++ b/mult/umult16.c
@@ -16,3 +16,16 @@ int umult16(uint16 a,uint16 b,uint16* c) {
 }
 
 #endif
+
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  uint16 a;
+  assert(umult16(7,10000,&a)==0);
+  assert(umult16(5,10,&a)==1 && a==50);
+  assert(umult16(6,10000,&a)==1 && a==60000);
+  return 0;
+}
+#endif
diff --git a/mult/umult32.c b/mult/umult32.c
index 948cf0f..557369d 100644
--- a/mult/umult32.c
+++ b/mult/umult32.c
@@ -16,3 +16,16 @@ int umult32(uint32 a,uint32 b,uint32* c) {
 }
 
 #endif
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  uint32 a;
+  assert(umult32(4,0x80000000,&a)==0);
+  assert(umult32(16,0x45000000,&a)==0);		// make sure we don't fall for "if a*b<a && a*b<b"
+  assert(umult32(5,10,&a)==1 && a==50);
+  assert(umult32(6,0x10000000,&a)==1 && a==0x60000000);
+  return 0;
+}
+#endif
diff --git a/mult/umult64.c b/mult/umult64.c
index c533b3d..84b6e4d 100644
--- a/mult/umult64.c
+++ b/mult/umult64.c
@@ -47,3 +47,16 @@ int umult64(uint64 a,uint64 b,uint64* c) {
 #endif
 
 #endif
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  uint64 a;
+  assert(umult64(4,0x8000000000000000ull,&a)==0);
+  assert(umult64(16,0x4500000000000000ull,&a)==0);		// make sure we don't fall for "if a*b<a && a*b<b"
+  assert(umult64(5,10,&a)==1 && a==50);
+  assert(umult64(0x60000000,0x10000000,&a)==1 && a==0x600000000000000);
+  return 0;
+}
+#endif
diff --git a/scan/scan_8int.c b/scan/scan_8int.c
index 41958d5..46f8a71 100644
--- a/scan/scan_8int.c
+++ b/scan/scan_8int.c
@@ -20,3 +20,18 @@ size_t scan_8int(const char* src,unsigned int* dest) {
   *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned int i;
+  assert(scan_8int("1234",&i)==4 && i==01234);
+  assert(scan_8int("12345678",&i)==7 && i==01234567);
+  assert(scan_8int("37777777777",&i)==11 && i==0xffffffff);
+  assert(scan_8int("40000000000",&i)==10 && i==04000000000);
+  assert(scan_8int("-4",&i)==0 && i==0);
+  assert(scan_8int("01234",&i)==5 && i==01234);
+  return 0;
+}
+#endif
diff --git a/scan/scan_8long.c b/scan/scan_8long.c
index 06283cc..d44c750 100644
--- a/scan/scan_8long.c
+++ b/scan/scan_8long.c
@@ -1,5 +1,31 @@
 #include "scan.h"
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "scan_8longn.c"
+#define UNITTEST
+#endif
+
 size_t scan_8long(const char *src,unsigned long *dest) {
   return scan_8longn(src,(size_t)-1,dest);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long i;
+  assert(scan_8long("1234",&i)==4 && i==01234);
+  assert(scan_8long("12345678",&i)==7 && i==01234567);
+  if (sizeof(long)==sizeof(int)) {
+    assert(scan_8long("37777777777",&i)==11 && i==0xffffffff);
+    assert(scan_8long("40000000000",&i)==10 && i==04000000000);
+  } else if (sizeof(long)==sizeof(long long)) {
+    assert(scan_8long("1777777777777777777777",&i)==22 && i==0xffffffffffffffffull);
+    assert(scan_8long("2000000000000000000000",&i)==21 && i==0200000000000000000000ull);
+  }
+  assert(scan_8long("-4",&i)==0 && i==0);
+  assert(scan_8long("01234",&i)==5 && i==01234);
+  return 0;
+}
+#endif
diff --git a/scan/scan_8longlong.c b/scan/scan_8longlong.c
index 3757a17..849e8c9 100644
--- a/scan/scan_8longlong.c
+++ b/scan/scan_8longlong.c
@@ -20,3 +20,18 @@ size_t scan_8longlong(const char *src,unsigned long long *dest) {
   *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long long i;
+  assert(scan_8longlong("1234",&i)==4 && i==01234);
+  assert(scan_8longlong("12345678",&i)==7 && i==01234567);
+  assert(scan_8longlong("1777777777777777777777",&i)==22 && i==0xffffffffffffffffull);
+  assert(scan_8longlong("2000000000000000000000",&i)==21 && i==200000000000000000000ull);
+  assert(scan_8longlong("-4",&i)==0 && i==0);
+  assert(scan_8longlong("01234",&i)==5 && i==01234);
+  return 0;
+}
+#endif
diff --git a/scan/scan_8longn.c b/scan/scan_8longn.c
index 31156fe..3bd2551 100644
--- a/scan/scan_8longn.c
+++ b/scan/scan_8longn.c
@@ -20,3 +20,24 @@ size_t scan_8longn(const char *src,size_t n,unsigned long *dest) {
   *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long i;
+  assert(scan_8longn("1234",100,&i)==4 && i==01234);
+  assert(scan_8longn("12345678",100,&i)==7 && i==01234567);
+  if (sizeof(long)==sizeof(int)) {
+    assert(scan_8longn("37777777777",100,&i)==11 && i==0xffffffff);
+    assert(scan_8longn("40000000000",100,&i)==10 && i==04000000000);
+  } else if (sizeof(long)==sizeof(long long)) {
+    assert(scan_8longn("1777777777777777777777",100,&i)==22 && i==0xffffffffffffffffull);
+    assert(scan_8longn("2000000000000000000000",100,&i)==21 && i==0200000000000000000000ull);
+  }
+  assert(scan_8longn("-4",100,&i)==0 && i==0);
+  assert(scan_8longn("01234",100,&i)==5 && i==01234);
+  assert(scan_8longn("1234",2,&i)==2 && i==012);
+  return 0;
+}
+#endif
diff --git a/scan/scan_8short.c b/scan/scan_8short.c
index 557087c..5549da8 100644
--- a/scan/scan_8short.c
+++ b/scan/scan_8short.c
@@ -22,3 +22,18 @@ size_t scan_8short(const char* src,unsigned short* dest) {
   *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned short i;
+  assert(scan_8short("1234",&i)==4 && i==01234);
+  assert(scan_8short("5678",&i)==3 && i==0567);
+  assert(scan_8short("177777",&i)==6 && i==0xffff);
+  assert(scan_8short("200000",&i)==5 && i==020000);
+  assert(scan_8short("-4",&i)==0 && i==0);
+  assert(scan_8short("01234",&i)==5 && i==01234);
+  return 0;
+}
+#endif
diff --git a/scan/scan_asn1derlength.c b/scan/scan_asn1derlength.c
index 557f555..864cd53 100644
--- a/scan/scan_asn1derlength.c
+++ b/scan/scan_asn1derlength.c
@@ -50,3 +50,29 @@ size_t scan_asn1derlength(const char* src,size_t len,unsigned long long* value)
   *value=l;
   return i;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long long i;
+  /* first check actual parsing */
+  assert(scan_asn1derlengthvalue("\x05",1,&i)==1 && i==5);
+  assert(scan_asn1derlengthvalue("\x81\xc2",2,&i)==2 && i==0xc2);
+  assert(scan_asn1derlengthvalue("\x82\x01\x23",3,&i)==3 && i==0x123);
+  assert(scan_asn1derlengthvalue("\x83\x01\x23\x45",4,&i)==4 && i==0x12345);
+  assert(scan_asn1derlengthvalue("\x83\x01\x23\x45",5,&i)==4 && i==0x12345);
+  assert(scan_asn1derlengthvalue("\x80",1,&i)==0);	// reject indefinite length encoding
+  assert(scan_asn1derlengthvalue("\x81\x05",2,&i)==0);	// reject non-minimal encoding
+  assert(scan_asn1derlengthvalue("\x81\xc2",1,&i)==0);	// reject truncated message
+  assert(scan_asn1derlengthvalue("\x82\xc2",2,&i)==0);	// reject truncated message
+  assert(scan_asn1derlengthvalue("\x82\x00\xc2",3,&i)==0);	// reject non-minimal encoding
+  assert(scan_asn1derlengthvalue("\x89\x01\x02\x03\x04\x05\x06\x07\x08\x09",10,&i)==0);	// value does not fit in target integer
+
+  /* now check buffer length checking in scan_asn1derlength */
+  assert(scan_asn1derlength("\x01",2,&i)==1 && i==1);	// ok
+  assert(scan_asn1derlength("\x02",2,&i)==0);		// buffer too small
+  assert(scan_asn1derlength("\x88\xff\xff\xff\xff\xff\xff\xff\xff",9,&i)==0);		// buffer too small, and integer overflow in naive check
+  return 0;
+}
+#endif
diff --git a/scan/scan_asn1dertag.c b/scan/scan_asn1dertag.c
index 769482d..9ab7fd7 100644
--- a/scan/scan_asn1dertag.c
+++ b/scan/scan_asn1dertag.c
@@ -25,3 +25,18 @@ size_t scan_asn1dertag(const char* src,size_t len,unsigned long long* length) {
   return 0;
 }
 
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long long i;
+  assert(scan_asn1dertag("\x00",1,&i)==1 && i==0);
+  assert(scan_asn1dertag("\x05",1,&i)==1 && i==5);
+  assert(scan_asn1dertag("\x81\x42",2,&i)==2 && i==0xc2);
+  assert(scan_asn1dertag("\x05",0,&i)==0);	// truncated
+  assert(scan_asn1dertag("\x81\x42",1,&i)==0);	// truncated
+  assert(scan_asn1dertag("\x80\x05",2,&i)==0);	// non-minimal encoding
+  assert(scan_asn1dertag("\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff",10,&i)==0);	// value does not fit
+  return 0;
+}
+#endif
diff --git a/scan/scan_charsetnskip.c b/scan/scan_charsetnskip.c
index 5d71aa5..9bc67b0 100644
--- a/scan/scan_charsetnskip.c
+++ b/scan/scan_charsetnskip.c
@@ -15,3 +15,15 @@ size_t scan_charsetnskip(const char *s,const char *charset,size_t limit) {
   }
   return (size_t)(t-s);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  assert(scan_charsetnskip("fnord","fo",4)==1);
+  assert(scan_charsetnskip("fnord","nf",4)==2);
+  assert(scan_charsetnskip("gaord","nf",4)==0);
+  assert(scan_charsetnskip("fnord","fnord",4)==4);
+  return 0;
+}
+#endif
diff --git a/scan/scan_fromhex.c b/scan/scan_fromhex.c
index 1365b39..8b52b28 100644
--- a/scan/scan_fromhex.c
+++ b/scan/scan_fromhex.c
@@ -18,3 +18,20 @@ int scan_fromhex(unsigned char c) {
 */
 }
 
+#ifdef UNITTEST
+#include <assert.h>
+int main() {
+  int i;
+  for (i=0; i<256; ++i) {
+    if (i>='0' && i<='9')
+      assert(scan_fromhex(i)==i-'0');
+    else if (i>='a' && i<='f')
+      assert(scan_fromhex(i)==i-'a'+10);
+    else if (i>='A' && i<='F')
+      assert(scan_fromhex(i)==i-'A'+10);
+    else
+      assert(scan_fromhex(i)==-1);
+  }
+  return 0;
+}
+#endif
diff --git a/scan/scan_int.c b/scan/scan_int.c
index 7b03548..93f809f 100644
--- a/scan/scan_int.c
+++ b/scan/scan_int.c
@@ -15,6 +15,10 @@ size_t scan_int(const char* src,int* dest) {
   }
   while ((c=(unsigned char)(*tmp-'0'))<10) {
     unsigned int n;
+#if defined(__GNUC__) && (__GNUC__ >= 5)
+    if (__builtin_mul_overflow(l,10,&n) || __builtin_add_overflow(n,c,&n))
+      break;
+#else
     /* we want to do: l=l*10+c
      * but we need to check for integer overflow.
      * to check whether l*10 overflows, we could do
@@ -27,6 +31,7 @@ size_t scan_int(const char* src,int* dest) {
     n+=(unsigned int)l<<1;
     if (n+c < n) break;
     n+=c;
+#endif
     if (n > maxint+neg) break;
     l=(int)n;
     ++tmp;
@@ -36,3 +41,20 @@ size_t scan_int(const char* src,int* dest) {
   *dest=(neg?-l:l);
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  int i;
+  assert(scan_int("1234",&i)==4 && i==1234);
+  assert(scan_int("-1234",&i)==5 && i==-1234);
+  assert(scan_int("+1234",&i)==5 && i==1234);
+  assert(scan_int("4294967295",&i)==9 && i==429496729);	// overflow
+  assert(scan_int("2147483647",&i)==10 && i==2147483647);	// MAX_INT
+  assert(scan_int("2147483648",&i)==9 && i==214748364);	// overflow
+  assert(scan_int("-2147483648",&i)==11 && i==-2147483648);	// MIN_INT
+  assert(scan_int("-2147483649",&i)==10 && i==-214748364);	// underflow
+  return 0;
+}
+#endif
diff --git a/scan/scan_long.c b/scan/scan_long.c
index ae610d9..308721d 100644
--- a/scan/scan_long.c
+++ b/scan/scan_long.c
@@ -1,5 +1,33 @@
 #include "scan.h"
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "scan_longn.c"
+#define UNITTEST
+#endif
+
 size_t scan_long(const char *src,long *dest) {
   return scan_longn(src,(size_t)(-1),dest);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  long i;
+  assert(scan_long("1234",&i)==4 && i==1234);
+  assert(scan_long("-1234",&i)==5 && i==-1234);
+  assert(scan_long("+1234",&i)==5 && i==1234);
+  assert(scan_long("2147483647",&i)==10 && i==2147483647);	// INT_MAX
+  assert(scan_long("-2147483648",&i)==11 && i==-2147483648);	// INT_MIN
+  if (sizeof(int) == sizeof(long)) {
+    assert(scan_long("4294967295",&i)==9 && i==429496729);	// overflow
+    assert(scan_long("2147483648",&i)==9 && i==214748364);	// overflow
+    assert(scan_long("-2147483649",&i)==10 && i==-214748364);	// underflow
+  } else {
+    assert(scan_long("9223372036854775807",&i)==19 && i==0x7fffffffffffffffull);	// LONG_MAX
+    assert(scan_long("-9223372036854775808",&i)==20 && i==(long long)0x8000000000000000ull);	// LONG_MIN
+  }
+  return 0;
+}
+#endif
diff --git a/scan/scan_longlong.c b/scan/scan_longlong.c
index 751733c..3d0934c 100644
--- a/scan/scan_longlong.c
+++ b/scan/scan_longlong.c
@@ -2,6 +2,12 @@
 
 static const unsigned long maxlong = ((unsigned long)-1)>>1;
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "scan_ulonglong.c"
+#define UNITTEST
+#endif
+
 size_t scan_longlong(const char* src,signed long long* dest) {
   size_t i,o;
   unsigned long long l;
@@ -17,3 +23,19 @@ size_t scan_longlong(const char* src,signed long long* dest) {
     return i+o;
   } return 0;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  long long i;
+  assert(scan_longlong("1234",&i)==4 && i==1234);
+  assert(scan_longlong("-1234",&i)==5 && i==-1234);
+  assert(scan_longlong("+1234",&i)==5 && i==1234);
+  assert(scan_longlong("2147483647",&i)==10 && i==2147483647);	// INT_MAX
+  assert(scan_longlong("-2147483648",&i)==11 && i==-2147483648);	// INT_MIN
+  assert(scan_longlong("9223372036854775807",&i)==19 && i==0x7fffffffffffffffull);	// LONG_MAX
+  assert(scan_longlong("-9223372036854775808",&i)==20 && i==(long long)0x8000000000000000ull);	// LONG_MIN
+  return 0;
+}
+#endif
diff --git a/scan/scan_longn.c b/scan/scan_longn.c
index 5543e69..f09ac40 100644
--- a/scan/scan_longn.c
+++ b/scan/scan_longn.c
@@ -16,6 +16,10 @@ size_t scan_longn(const char *src,size_t n,long *dest) {
   }
   while (n-->0 && (c=(unsigned char)(*tmp-'0'))<10) {
     unsigned long int n;
+#if defined(__GNUC__) && (__GNUC__ >= 5)
+    if (__builtin_mul_overflow(l,10,&n) || __builtin_add_overflow(n,c,&n))
+      break;
+#else
     /* we want to do: l=l*10+c
      * but we need to check for integer overflow.
      * to check whether l*10 overflows, we could do
@@ -28,6 +32,7 @@ size_t scan_longn(const char *src,size_t n,long *dest) {
     n+=(unsigned long)l<<1;
     if (n+c < n) break;
     n+=c;
+#endif
     if (n > maxlong+neg) break;
     l=(long)n;
     ++tmp;
diff --git a/scan/scan_netstring.c b/scan/scan_netstring.c
index d7d3e26..8ef57f4 100644
--- a/scan/scan_netstring.c
+++ b/scan/scan_netstring.c
@@ -23,3 +23,20 @@ size_t scan_netstring(const char* in,size_t len,char** dest,size_t* slen) {
   *slen=l;
   return n+2+l;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+#include "scan_ulongn.c"
+
+int main() {
+  char buf[]="12:hello world!,";
+  char* s;
+  size_t l;
+  const char* orig;
+  assert(scan_netstring(buf,16,&s,&l)==16 && s==buf+3 && l==12);
+
+  orig="3:foo,"; assert(scan_netstring(orig,6,&s,&l)==6 && s==orig+2 && l==3);
+  orig="4294967295:foo,"; assert(scan_netstring(orig,15,&s,&l)==0);
+  orig="18446744073709551615:foo,"; assert(scan_netstring(orig,25,&s,&l)==0);
+}
+#endif
diff --git a/scan/scan_short.c b/scan/scan_short.c
index b35a0aa..ec9ecc4 100644
--- a/scan/scan_short.c
+++ b/scan/scan_short.c
@@ -15,6 +15,10 @@ size_t scan_short(const char* src,short* dest) {
   }
   while ((c=(unsigned char)(*tmp-'0'))<10) {
     unsigned short int n;
+#if defined(__GNUC__) && (__GNUC__ >= 5)
+    if (__builtin_mul_overflow(l,10,&n) || __builtin_add_overflow(n,c,&n))
+      break;
+#else
     /* we want to do: l=l*10+c
      * but we need to check for integer overflow.
      * to check whether l*10 overflows, we could do
@@ -27,6 +31,7 @@ size_t scan_short(const char* src,short* dest) {
     n=(unsigned short)(n+(l<<1));
     if (n+c < n) break;
     n=(unsigned short)(n+c);
+#endif
     if (n > maxshort+neg) break;
     l=(short)n;
     ++tmp;
diff --git a/scan/scan_ulonglong.c b/scan/scan_ulonglong.c
index 23cd8eb..3b03a80 100644
--- a/scan/scan_ulonglong.c
+++ b/scan/scan_ulonglong.c
@@ -6,14 +6,34 @@ size_t scan_ulonglong(const char *src,unsigned long long *dest) {
   register unsigned char c;
   while ((c=(unsigned char)(*tmp-'0'))<10) {
     unsigned long long n;
+#if defined(__GNUC__) && (__GNUC__ >= 5)
+    if (__builtin_mul_overflow(l,10,&n) || __builtin_add_overflow(n,c,&n))
+      break;
+    l=n;
+#else
     /* division is very slow on most architectures */
     n=l<<3; if ((n>>3)!=l) break;
     if (n+(l<<1) < n) break;
     n+=l<<1;
     if (n+c < n) break;
     l=n+c;
+#endif
     ++tmp;
   }
   if (tmp-src) *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long long l;
+  assert(scan_ulonglong("0",&l)==1 && l==0);
+  assert(scan_ulonglong("1",&l)==1 && l==1);
+  assert(scan_ulonglong("4294967295",&l) == 10 && l==4294967295ull);
+  assert(scan_ulonglong("18446744073709551615",&l) == 20 && l==18446744073709551615ull);
+  assert(scan_ulonglong("18446744073709551616",&l) == 19 && l==1844674407370955161ull);
+  return 0;
+}
+#endif
diff --git a/scan/scan_ulongn.c b/scan/scan_ulongn.c
index 1255b9a..ad45f65 100644
--- a/scan/scan_ulongn.c
+++ b/scan/scan_ulongn.c
@@ -8,6 +8,21 @@ size_t scan_ulongn(const char* src,size_t n,unsigned long int* dest) {
   /* Since the conditions can be computed at compile time, the compiler
    * should only emit code for one of the implementations, depending on
    * which architecture the code is compiled for. */
+#if defined(__GNUC__) && (__GNUC__ >= 5)
+  /* implementation for recent gcc or clang */
+  int ok=0;
+  for (; n-->0 && (c=(unsigned char)(*tmp-'0'))<10; ++tmp) {
+    unsigned long v;
+    if (__builtin_mul_overflow(l,10,&v) || __builtin_add_overflow(v,c,&v))
+      break;
+    l=v;
+    ok=1;
+  }
+  if (!ok) return 0;
+
+  *dest=l;
+  return (size_t)(tmp-src);
+#else
 #ifdef HAVE_UINT128
   if (sizeof(unsigned long)==sizeof(unsigned long long) && sizeof(unsigned long)<sizeof(__uint128_t)) {
     /* implementation for 64-bit platforms with gcc */
@@ -48,4 +63,22 @@ size_t scan_ulongn(const char* src,size_t n,unsigned long int* dest) {
     if (tmp-src) *dest=l;
     return (size_t)(tmp-src);
   }
+#endif
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long l;
+  assert(scan_ulongn("4294967295",10,&l) == 10 && l==4294967295ul);
+  if (sizeof(unsigned long)==4) {
+    assert(scan_ulongn("4294967296",10,&l) == 9 && l==429496729);
+  } else {
+    assert(scan_ulongn("18446744073709551615",20,&l) == 20 && l==18446744073709551615ull);
+    assert(scan_ulongn("18446744073709551616",20,&l) == 19 && l==1844674407370955161ull);
+  }
+  assert(scan_ulongn("1234",3,&l)==3 && l==123);
+  return 0;
+}
+#endif
diff --git a/scan/scan_ushort.c b/scan/scan_ushort.c
index fa8aaf8..eb78e6c 100644
--- a/scan/scan_ushort.c
+++ b/scan/scan_ushort.c
@@ -29,3 +29,17 @@ size_t scan_ushort(const char* src,unsigned short* dest) {
     (void)compileerror;
   }
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned short i;
+  assert(scan_ushort("1234",&i)==4 && i==1234);
+  assert(scan_ushort("-1",&i)==0);
+  if (sizeof(short)==2) {
+    assert(scan_ushort("123456",&i)==5 && i==12345);
+  }
+  return 0;
+}
+#endif
diff --git a/scan/scan_utf8.c b/scan/scan_utf8.c
index f668e0b..3942841 100644
--- a/scan/scan_utf8.c
+++ b/scan/scan_utf8.c
@@ -50,3 +50,74 @@ size_t scan_utf8(const char* in,size_t len,uint32_t* num) {
   return (size_t)(in-orig);
 }
 
+#ifdef UNITTEST
+#include <assert.h>
+#include "fmt/fmt_utf8.c"
+
+int main() {
+  char buf[100];
+  uint32_t l;
+  unsigned int i;
+  /* first positive testing for the various lengths */
+  l=fmt_utf8(buf,0); assert(l == 1 && scan_utf8(buf,l+1,&l)==1 && l==0);
+  l=fmt_utf8(buf,0x80); assert(l == 2 && scan_utf8(buf,l+1,&l)==2 && l==0x80);
+  l=fmt_utf8(buf,0x800); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0x800);
+  l=fmt_utf8(buf,0x10000); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x10000);
+  l=fmt_utf8(buf,0x200000); assert(l == 5 && scan_utf8(buf,l+1,&l)==5 && l==0x200000);
+  l=fmt_utf8(buf,0x4000000); assert(l == 6 && scan_utf8(buf,l+1,&l)==6 && l==0x4000000);
+  /* corner cases */
+  l=fmt_utf8(buf,0x7f); assert(l == 1 && scan_utf8(buf,l+1,&l)==1 && l==0x7f);
+  l=fmt_utf8(buf,0x7ff); assert(l == 2 && scan_utf8(buf,l+1,&l)==2 && l==0x7ff);
+  l=fmt_utf8(buf,0xffff); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xffff);
+  l=fmt_utf8(buf,0x1fffff); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x1fffff);
+  l=fmt_utf8(buf,0x3ffffff); assert(l == 5 && scan_utf8(buf,l+1,&l)==5 && l==0x3ffffff);
+  l=fmt_utf8(buf,0x7fffffff); assert(l == 6 && scan_utf8(buf,l+1,&l)==6 && l==0x7fffffff);
+  /* more corner cases */
+  l=fmt_utf8(buf,0xd7ff); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xd7ff);
+  l=fmt_utf8(buf,0xe000); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xe000);
+  l=fmt_utf8(buf,0xfffd); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xfffd);
+  l=fmt_utf8(buf,0x10ffff); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x10ffff);
+  l=fmt_utf8(buf,0x110000); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x110000);
+
+  /* now negative testing */
+  /* start off with some continuation bytes outside a sequence */
+  for (i=0x80; i<=0xbf; ++i) {
+    buf[0]=i;
+    assert(scan_utf8(buf,2,&l)==0);
+  }
+
+  /* now check lonely sequence start characters */
+  buf[1]=' ';
+  for (i=0xc0; i<=0xfd; ++i) {
+    buf[0]=i;
+    assert(scan_utf8(buf,2,&l)==0);
+  }
+
+  /* FE and FF are reserved for UTF-16 endianness detection*/
+  assert(scan_utf8("\xfe\xff",3,&l)==0);
+  assert(scan_utf8("\xff\xfe",3,&l)==0);
+
+  /* now check some truncated sequences */
+  l=fmt_utf8(buf,0); assert(l == 1 && scan_utf8(buf,l-1,&l)==0);
+  l=fmt_utf8(buf,0x80); assert(l == 2 && scan_utf8(buf,l-1,&l)==0);
+  l=fmt_utf8(buf,0x800); assert(l == 3 && scan_utf8(buf,l-1,&l)==0);
+  l=fmt_utf8(buf,0x10000); assert(l == 4 && scan_utf8(buf,l-1,&l)==0);
+  l=fmt_utf8(buf,0x200000); assert(l == 5 && scan_utf8(buf,l-1,&l)==0);
+  l=fmt_utf8(buf,0x4000000); assert(l == 6 && scan_utf8(buf,l-1,&l)==0);
+
+  /* now truncate in another way */
+  l=fmt_utf8(buf,0x80); buf[l-1]=' '; assert(l == 2 && scan_utf8(buf,l+1,&l)==0);
+  l=fmt_utf8(buf,0x800); buf[l-1]=' '; assert(l == 3 && scan_utf8(buf,l+1,&l)==0);
+  l=fmt_utf8(buf,0x10000); buf[l-1]=' '; assert(l == 4 && scan_utf8(buf,l+1,&l)==0);
+  l=fmt_utf8(buf,0x200000); buf[l-1]=' '; assert(l == 5 && scan_utf8(buf,l+1,&l)==0);
+  l=fmt_utf8(buf,0x4000000); buf[l-1]=' '; assert(l == 6 && scan_utf8(buf,l+1,&l)==0);
+
+  /* now some not minimally encoded utf-8 sequences */
+  assert(scan_utf8("\xc0\x80",3,&l)==0);
+  assert(scan_utf8("\xe0\x80\x80",4,&l)==0);
+  assert(scan_utf8("\xf0\x80\x80\x80",5,&l)==0);
+  assert(scan_utf8("\xf8\x80\x80\x80\x80",6,&l)==0);
+  assert(scan_utf8("\xfc\x80\x80\x80\x80\x80",7,&l)==0);
+  return 0;
+}
+#endif
diff --git a/scan/scan_utf8_sem.c b/scan/scan_utf8_sem.c
index 451166e..36fc368 100644
--- a/scan/scan_utf8_sem.c
+++ b/scan/scan_utf8_sem.c
@@ -9,3 +9,13 @@ size_t scan_utf8_sem(const char* in,size_t len,uint32_t* num) {
   }
   return r;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  /* rest of scan_utf8 tested in scan_utf8.c unit tests */
+  assert(scan_utf8_sem("\xed\xa0\x80",4,&l)==0);
+  return 0;
+}
+#endif
diff --git a/scan/scan_varint.c b/scan/scan_varint.c
index fd15576..ca78bd7 100644
--- a/scan/scan_varint.c
+++ b/scan/scan_varint.c
@@ -5,8 +5,11 @@ size_t scan_varint(const char* in,size_t len, unsigned long long* n) {
   unsigned long long l;
   if (len==0) return 0;
   for (l=0, i=0; i<len; ++i) {
+    if (i*7+7>sizeof(l)*8)	// value too large to fit in destination integer!
+      return 0;
     l+=(unsigned long long)(in[i]&0x7f) << (i*7);
     if (!(in[i]&0x80)) {
+      if (in[i]==0) return 0;	// libowfat extension: reject non-minimal encoding
       *n=l;
       return i+1;
     }
@@ -21,3 +24,16 @@ size_t scan_pb_type0_int(const char* dest,size_t len,unsigned long long* l) {
   return scan_varint(dest,len,l);
 }
 #endif
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long long n;
+  assert(scan_varint("\x05",1,&n)==1 && n==5);
+  assert(scan_varint("\x80\x00",2,&n)==0);	// non-minimal encoding
+  assert(scan_varint("\x80\x80",2,&n)==0);	// truncated (last byte in sequence has high bit 0)
+  assert(scan_varint("\x80\x80\x80\x80\x80\x80\x80\x80\x80\x01",10,&n)==0);	// value too large
+  return 0;
+}
+#endif
diff --git a/scan/scan_whitenskip.c b/scan/scan_whitenskip.c
index 3297f0a..634ae85 100644
--- a/scan/scan_whitenskip.c
+++ b/scan/scan_whitenskip.c
@@ -7,3 +7,15 @@ size_t scan_whitenskip(const char *s,size_t limit) {
   while (t<u && isspace(*t)) ++t;
   return (size_t)(t-s);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  assert(scan_whitenskip("foo",3)==0);
+  assert(scan_whitenskip(" foo",4)==1);
+  assert(scan_whitenskip("  foo",1)==1);
+  assert(scan_whitenskip("  foo",2)==2);
+  return 0;
+}
+#endif
diff --git a/scan/scan_xint.c b/scan/scan_xint.c
index 316c059..5a11f7e 100644
--- a/scan/scan_xint.c
+++ b/scan/scan_xint.c
@@ -1,5 +1,11 @@
 #include "scan.h"
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "scan_fromhex.c"
+#define UNITTEST
+#endif
+
 size_t scan_xint(const char* src,unsigned int* dest) {
   register const char *tmp=src;
   register unsigned int l=0;
@@ -11,3 +17,17 @@ size_t scan_xint(const char* src,unsigned int* dest) {
   *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned int i;
+  assert(scan_xint("fefe",&i)==4 && i==0xfefe);
+  assert(scan_xint("0xfefe",&i)==1);	// 0x not supported, will scan the 0
+  assert(scan_xint("+fefe",&i)==0);
+  assert(scan_xint("fefec0de",&i)==8 && i==0xfefec0de);
+  assert(scan_xint("fefec0debaad",&i)==8 && i==0xfefec0de);	// test truncation
+  return 0;
+}
+#endif
diff --git a/scan/scan_xlong.c b/scan/scan_xlong.c
index b0e9e05..8cda884 100644
--- a/scan/scan_xlong.c
+++ b/scan/scan_xlong.c
@@ -3,3 +3,5 @@
 size_t scan_xlong(const char *src,unsigned long *dest) {
   return scan_xlongn(src,(size_t)-1,dest);
 }
+
+/* unit tested via scan_xlongn */
diff --git a/scan/scan_xlongn.c b/scan/scan_xlongn.c
index e29f574..181196e 100644
--- a/scan/scan_xlongn.c
+++ b/scan/scan_xlongn.c
@@ -1,5 +1,11 @@
 #include "scan.h"
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "scan_fromhex.c"
+#define UNITTEST
+#endif
+
 size_t scan_xlongn(const char *src,size_t n,unsigned long *dest) {
   register const char *tmp=src;
   register unsigned long l=0;
@@ -11,3 +17,22 @@ size_t scan_xlongn(const char *src,size_t n,unsigned long *dest) {
   *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned long i;
+  assert(scan_xlongn("fefe",4,&i)==4 && i==0xfefe);
+  assert(scan_xlongn("0xfefe",6,&i)==1);	// 0x not supported, will scan the 0
+  assert(scan_xlongn("+fefe",5,&i)==0);
+  assert(scan_xlongn("fefec0de",7,&i)==7 && i==0xfefec0d);
+  assert(scan_xlongn("fefec0de",8,&i)==8 && i==0xfefec0de);
+  assert(scan_xlongn("fefec0de",9,&i)==8 && i==0xfefec0de);
+  if (sizeof(i)==4)
+    assert(scan_xlongn("fefec0debaad",14,&i)==8 && i==0xfefec0de);	// test truncation
+  else if (sizeof(i)==8)
+    assert(scan_xlongn("fefec0debaadc0debl06",40,&i)==16 && i==0xfefec0debaadc0de);	// test truncation
+  return 0;
+}
+#endif
diff --git a/scan/scan_xshort.c b/scan/scan_xshort.c
index 53b8f95..f7659da 100644
--- a/scan/scan_xshort.c
+++ b/scan/scan_xshort.c
@@ -1,5 +1,11 @@
 #include "scan.h"
 
+#ifdef UNITTEST
+#undef UNITTEST
+#include "scan_fromhex.c"
+#define UNITTEST
+#endif
+
 size_t scan_xshort(const char* src,unsigned short* dest) {
   register const char *tmp=src;
   register unsigned short l=0;
@@ -11,3 +17,16 @@ size_t scan_xshort(const char* src,unsigned short* dest) {
   *dest=l;
   return (size_t)(tmp-src);
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  unsigned short i;
+  assert(scan_xshort("fefe",&i)==4 && i==0xfefe);
+  assert(scan_xshort("0xfefe",&i)==1);	// 0x not supported, will scan the 0
+  assert(scan_xshort("+fefe",&i)==0);
+  assert(scan_xshort("fefec0de",&i)==4 && i==0xfefe);	// test truncation
+  return 0;
+}
+#endif
diff --git a/textcode/scan_base64.c b/textcode/scan_base64.c
index 8affddd..6fdc5c7 100644
--- a/textcode/scan_base64.c
+++ b/textcode/scan_base64.c
@@ -50,5 +50,6 @@ int main() {
   memset(buf,0,10); assert(scan_base64("Zm5vcmQ=",buf,&l)==8 && l==5 && !memcmp(buf,"fnord",6));
   memset(buf,0,10); assert(scan_base64("Zm5vcmQ",buf,&l)==7 && l==5 && !memcmp(buf,"fnord",6));
   memset(buf,0,10); assert(scan_base64("//8=",buf,&l)==4 && l==2 && !memcmp(buf,"\xff\xff",3));
+  return 0;
 }
 #endif
diff --git a/textcode/scan_jsonescape.c b/textcode/scan_jsonescape.c
index ae3bc61..786f2c0 100644
--- a/textcode/scan_jsonescape.c
+++ b/textcode/scan_jsonescape.c
@@ -101,5 +101,6 @@ int main() {
   assert(scan_jsonescape("a\\ud834\\udd1eb",buf,&l)==14 && l==6 && !memcmp(buf,"a\xf0\x9d\x84\x9e""b",6));
   /* how about some incorrect UTF-8? */
   assert(scan_jsonescape("a\xc0\xaf",buf,&l)==1 && l==1 && !memcmp(buf,"a",1));
+  return 0;
 }
 #endif
diff --git a/textcode/scan_uuencoded.c b/textcode/scan_uuencoded.c
index af6f2f0..703ec93 100644
--- a/textcode/scan_uuencoded.c
+++ b/textcode/scan_uuencoded.c
@@ -36,6 +36,7 @@ int main() {
   assert(scan_uuencoded("&9FYO<F0*",buf,&i)==9 && i==6 && !memcmp(buf,"fnord\n",7));
   memset(buf,0,100);
   assert(scan_uuencoded("%9FYO<F0`",buf,&i)==9 && i==5 && !memcmp(buf,"fnord",6));
+  return 0;
 }
 
 #endif