add some int overflow check macros to rangecheck.h

CHANGES

@@ -3,6 +3,7 @@
     start over from the beginning because always new accept()ed
     connections came in and got newer, higher descriptors since the last
     io_timeouted loop.  (Dirk Engling)
+  add some int overflow check macros to rangecheck.h
 
 0.25:
   array_allocate no longer truncates the array

rangecheck.h

@@ -54,6 +54,43 @@ int range_str2inbuf(const void* buf,size_t len,const void* stringstart);
 /* does an UTF-32 string starting at "ptr" lie in buf[0..len-1]? */
 int range_str4inbuf(const void* buf,size_t len,const void* stringstart);
 
+
+/* I originally omitted addition and substraction because it appeared
+ * trivial.  You could just add the two numbers and see if it was
+ * smaller than either of them.  This always worked for me because I
+ * only cared about unsigned arithmetic, but for signed arithmetic,
+ * adding two numbers is undefined if the result does not fit in the
+ * int.  gcc has started to actually use this undefinedness to screw
+ * you.  The following code illustrates this:
+ *   int a=INT_MAX,b=a+5;
+ *   if (b<a) abort();  // whole statement optimized away by gcc 4.1
+ *   // at this point, b<a
+ * So I decided to add some integer overflow protection functionality
+ * here for addition and subtraction, too. */
+
+/* first, we need a type independent way to find the min and max values
+ * for each type, so the macros also work for integer types you defined
+ * yourself */
+
+#define __MIN_UNSIGNED(type) ((type)0)
+#define __MIN_SIGNED(type) (((type)-1)<<(sizeof(type)*8-1))
+
+#define __MAX_UNSIGNED(type) (((type)-1))
+#define __MAX_SIGNED_TEMP(type) (((type)1)<<(sizeof(type)*8-2))
+#define __MAX_SIGNED(type) (__MAX_SIGNED_TEMP(type)+(__MAX_SIGNED_TEMP(type)-1))
+
+/* we use <1 and not <0 to avoid a gcc warning */
+#define __MAX(type) ((type)-1 < 1?__MAX_SIGNED(type):__MAX_UNSIGNED(type))
+#define __MIN(type) ((type)-1 < 1?__MIN_SIGNED(type):__MIN_UNSIGNED(type))
+
+#define assign(dest,src) ({ typeof(src) __x=src; typeof(dest) __y=__x; (__x==__y && ((__x<1) == (__y<1))?(int)(dest=__y),0:1); })
+
+/* if a+b is defined and does not have an integer overflow, do c=a+b and
+ * return 0.  Otherwise, return 1. */
+#define add_of(c,a,b) ({ typeof(a) __a=a; typeof(b) __b=b; (__b)<1?((__MIN(typeof(c))-(__b)<=(__a))?assign(c,__a+__b):1) : ((__MAX(typeof(c))-(__b)>=(__a))?assign(c,__a+__b):1); })
+
+#define sub_of(c,a,b) ({ typeof(a) __a=a; typeof(b) __b=b; (__b)<1?((__MAX(typeof(c))-(__b)>=(__a))?assign(c,__a-__b):1) : ((__MIN(typeof(c))+(__b)<=(__a))?assign(c,__a-__b):1); })
+
 #undef __static
 
 #endif

test/range.c

@@ -1,8 +1,54 @@
 #include "rangecheck.h"
 #include <assert.h>
 #include <stdio.h>
+#include <inttypes.h>
+#include <limits.h>
 
-int main() {
+void check_minmax() {
+  /* make sure the __MIN and __MAX macros work */
+  assert(__MIN(signed char)==-128);
+  assert(__MAX(signed char)==127);
+  assert(__MIN(unsigned char)==0);
+  assert(__MAX(unsigned char)==255);
+
+  assert(__MIN(short)==SHRT_MIN);
+  assert(__MAX(short)==SHRT_MAX);
+  assert(__MIN(unsigned short)==0);
+  assert(__MAX(unsigned short)==USHRT_MAX);
+
+  assert(__MIN(int)==INT_MIN);
+  assert(__MAX(int)==INT_MAX);
+  assert(__MIN(unsigned int)==0);
+  assert(__MAX(unsigned int)==UINT_MAX);
+
+  assert(__MIN(long)==LONG_MIN);
+  assert(__MAX(long)==LONG_MAX);
+  assert(__MIN(unsigned long)==0);
+  assert(__MAX(unsigned long)==ULONG_MAX);
+
+#ifdef LLONG_MIN
+  assert(__MIN(long long)==LLONG_MIN);
+  assert(__MAX(long long)==LLONG_MAX);
+  assert(__MIN(unsigned long long)==0);
+  assert(__MAX(unsigned long long)==ULLONG_MAX);
+#endif
+
+  assert(__MIN(int32_t)==(int32_t)0x80000000);
+  assert(__MAX(int32_t)==0x7fffffff);
+  assert(__MIN(uint32_t)==0);
+  assert(__MAX(uint32_t)==0xffffffff);
+}
+
+void check_assign() {
+  int a;
+  assert(assign(a,5)==0 && a==5);
+  a=23; assert(assign(a,(unsigned int)-23)==1);
+#ifdef LLONG_MIN
+  a=23; assert(assign(a,LLONG_MAX)==1);
+#endif
+}
+
+void check_rangeptrbuf() {
   char buf[1000];
 
   /* does range_ptrinbuf check all the incoming pointer cases right? */
@@ -83,7 +129,75 @@ int main() {
     assert(range_str4inbuf(y,sizeof(y),y+5)==1);
     assert(range_str4inbuf(y,sizeof(y),y+6)==0);
   }
+}
+
+void check_intof() {
+  /* since the macros are type independent, we only check one signed and
+   * one unsigned type */
+
+  /* some checks are redundant, but we want to cover off-by-one cases */
+  {
+    int a;
+    a=0; assert(add_of(a,INT_MAX-3,1)==0 && a==INT_MAX-2);
+    a=0; assert(add_of(a,INT_MAX-3,5)==1);
+    a=0; assert(add_of(a,INT_MAX-3,3)==0 && a==INT_MAX);
+    a=0; assert(add_of(a,INT_MAX-3,4)==1);
+    a=0; assert(add_of(a,0,INT_MIN)==0 && a==INT_MIN);
+    a=0; assert(add_of(a,-1,INT_MIN)==1);
+    a=0; assert(add_of(a,1,INT_MAX)==1);
+
+    /* now let's see what happens if the addition has a wider data
+     * type than the destionation */
+    a=0; assert(add_of(a,0x100000000ll,-0x80000000ll)==1);
+    a=0; assert(add_of(a,0x100000000ll,-0x80000001ll)==0 && a==0x7fffffff);
+    a=0; assert(add_of(a,0x100000000ll,-10)==1);
+    a=0; assert(add_of(a,-0x90000000ll,0x10000000)==0 && a==0x80000000);
+
+    /* what if we add two ints, the result does not overflow but is
+     * still negative, but we assign it to an unsigned int? */
+    a=0; assert(add_of(a,0x7ffffff0,0x10)==1);
+  }
+
+  {
+    unsigned int a;
+    a=0; assert(add_of(a,UINT_MAX-3,1)==0 && a==UINT_MAX-2);
+    a=0; assert(add_of(a,UINT_MAX-3,5)==1);
+    a=0; assert(add_of(a,UINT_MAX-3,4)==1);
+    a=0; assert(add_of(a,2,-3)==1);
+    a=23; assert(add_of(a,2,-2)==0 && a==0);
+    a=0; assert(add_of(a,(int)0x80000000,(int)-2147483648)==0 && a==0);
+    a=0; assert(add_of(a,(int)0x7fffffff,(int)-2147483648)==1);
+    a=0; assert(add_of(a,1,UINT_MAX)==1);
+
+    /* now let's see what happens if the addition has a wider data
+     * type than the destionation */
+    a=0; assert(add_of(a,0x100000000ll,-5)==0 && a==4294967291);
+    a=0; assert(add_of(a,-0x100000010ll,5)==1);
+    a=0; assert(add_of(a,0x100000010ll,-5)==1);
+
+    /* what if we add two ints, the result does not overflow but is
+     * still negative, but we assign it to an unsigned int? */
+    a=0; assert(add_of(a,-10,-5)==1);
+  }
+
+  {
+    int a;
+    a=0; assert(sub_of(a,10,5)==0 && a==5);
+    a=0; assert(sub_of(a,5,10)==0 && a==-5);
+    a=0; assert(sub_of(a,INT_MIN,10)==1);
+    a=0; assert(sub_of(a,INT_MIN,-10)==0 && a==INT_MIN+10);
+    a=0; assert(sub_of(a,INT_MAX,-10)==1);
+    a=0; assert(sub_of(a,INT_MAX,10)==0 && a==INT_MAX-10);
+  }
+
+}
+
+int main() {
 
+  check_minmax();
+  check_assign();
+  check_intof();
+  check_rangeptrbuf();
 
   puts("all tests ok");
   return 0;