slight optimization

scan/scan_fromhex.c

@@ -1,6 +1,13 @@
 #include "scan.h"
 
 int scan_fromhex(unsigned char c) {
+  c-='0';
+  if (c<=9) return c;
+  c&=~0x20;
+  c-='A'-'0';
+  if (c<6) return c+10;
+  return -1;
+/* more readable but creates worse code:
   if (c>='0' && c<='9')
     return c-'0';
   else if (c>='A' && c<='F')
@@ -8,5 +15,6 @@ int scan_fromhex(unsigned char c) {
   else if (c>='a' && c<='f')
     return c-'a'+10;
   return -1;
+*/
 }