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add skip_prefix_mem helper

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The skip_prefix function has been very useful for
simplifying pointer arithmetic and avoiding repeated magic
numbers, but we have no equivalent for length-limited
buffers. So we're stuck with:

  if (3 <= len && skip_prefix(buf, "foo", &buf))
	  len -= 3;

That's not that complicated, but it needs to use magic
numbers for the length of the prefix (or else write out
strlen("foo"), repeating the string). By using a helper, we
can get the string length behind the scenes (and often at
compile time for string literals).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2016-06-23 13:33:57 -04:00 committed by Junio C Hamano
parent adb3356664
commit ae989a61da
1 changed files with 17 additions and 0 deletions
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17
git-compat-util.h
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@ -463,6 +463,23 @@ static inline int skip_prefix(const char *str, const char *prefix,
return 0;
}
/*
* Like skip_prefix, but promises never to read past "len" bytes of the input
* buffer, and returns the remaining number of bytes in "out" via "outlen".
*/
static inline int skip_prefix_mem(const char *buf, size_t len,
const char *prefix,
const char **out, size_t *outlen)
{
size_t prefix_len = strlen(prefix);
if (prefix_len <= len && !memcmp(buf, prefix, prefix_len)) {
*out = buf + prefix_len;
*outlen = len - prefix_len;
return 1;
}
return 0;
}
/*
* If buf ends with suffix, return 1 and subtract the length of the suffix
* from *len. Otherwise, return 0 and leave *len untouched.