Fix some overlap mismatch

This was caught by the following test:

```

int main(void) {
    char c[32];
    memcpy(c, c + 16, 16);
}
```

Reported-by: q66

2 files changed, 5 insertions, 7 deletions

diff --git a/include/fortify-headers.h b/include/fortify-headers.h
index ea2e430..796fd2d 100644
--- a/include/fortify-headers.h
+++ b/include/fortify-headers.h
@@ -141,8 +141,8 @@
  * since gcc seems to like to generate code that relies on dst == src */
 #define __fh_overlap(a, len_a, b, len_b) \
         ( \
-                ((a) < (b) && (b) < (a) + (__fh_size_t)(len_a)) \
-             || ((b) < (a) && (a) < (b) + (__fh_size_t)(len_b)) \
+                ((a) < (b) && (b) < ((a) + (__fh_size_t)(len_a))) \
+             || ((b) < (a) && (a) < ((b) + (__fh_size_t)(len_b))) \
         )
 
 /*
diff --git a/include/string.h b/include/string.h
index 071d592..924be49 100644
--- a/include/string.h
+++ b/include/string.h
@@ -58,10 +58,8 @@ __error_if((__fh_bos(__od, 0) < __n), "'memcpy' called with `n` bigger than the
 
         __fh_size_t __bd = __fh_bos(__od, 0);
         __fh_size_t __bs = __fh_bos(__os, 0);
-        char *__d = (char *)__od;
-        const char *__s = (const char *)__os;
 
-        if __fh_overlap(__d, __bd, __s, __n)
+        if __fh_overlap(__od, __n, __os, __n)
                 __builtin_trap();
         if (__n > __bd || __n > __bs)
                 __builtin_trap();
@@ -189,7 +187,7 @@ _FORTIFY_FN(stpcpy) char *stpcpy(char * _FORTIFY_POS0 __d, const char *__s)
         __fh_size_t __n = strlen(__s) + 1;
         __fh_size_t __b = __fh_bos(__d, 0);
 
-        if (__fh_overlap(__d, __b, __s, __n))
+        if (__fh_overlap(__d, __n, __s, __n))
                 __builtin_trap();
 
         if (__n > __b)
@@ -257,7 +255,7 @@ _FORTIFY_FN(strcpy) char *strcpy(char * _FORTIFY_POS0 __d, const char *__s)
         __fh_size_t __n = strlen(__s) + 1;
         __fh_size_t __b = __fh_bos(__d, 0);
 
-        if (__fh_overlap(__d, __b, __s, __n))
+        if (__fh_overlap(__d, __n, __s, __n))
                 __builtin_trap();
 
         if (__n > __b)