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Date: Tue, 13 Jul 2021 14:02:06 +0200
From: "Stefan Kanthak" <stefan.kanthak@...go.de>
To: <musl@...ts.openwall.com>
Subject: Changes for strcspn(), strspn(), strtok() and strtok_r()
<https://git.musl-libc.org/cgit/musl/plain/src/string/strcspn.c>
#include <string.h>
#define BITOP(a,b,op) \
((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
-size_t strcspn(const char *s, const char *c)
+size_t strcspn(const char *restrict s, const char *c)
{
- const char *a = s;
+ const char *a;
- size_t byteset[32/sizeof(size_t)];
+ size_t byteset[32/sizeof(size_t)] = { 0 };
- if (!c[0] || !c[1]) return __strchrnul(s, *c)-a;
+ if (!c[0] || !c[1]) return __strchrnul(a=s, *c)-a;
- memset(byteset, 0, sizeof byteset);
for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
- for (; *s && !BITOP(byteset, *(unsigned char *)s, &); s++);
- return s-a;
+ for (a=s; *a && !BITOP(byteset, *(unsigned char *)a, &); a++);
+ return a-s;
}
After this change, musl's favorite compiler (GCC) will generate code
like the following (here for x86-64), just like the code it already
generates for strspn(), where the initialization of byteset[] is NOT
done via memset():
strcspn:
...
xor %eax, %eax
movq %rax, byteset(%rsp)
movq %rax, byteset+8(%rsp)
movq %rax, byteset+16(%rsp)
movq %rax, byteset+24(%rsp)
...
<https://git.musl-libc.org/cgit/musl/plain/src/string/strspn.c>
#include <string.h>
#define BITOP(a,b,op) \
((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
-size_t strspn(const char *s, const char *c)
+size_t strspn(const char *restrict s, const char *c)
{
- const char *a = s;
+ const char *a;
size_t byteset[32/sizeof(size_t)] = { 0 };
if (!c[0]) return 0;
if (!c[1]) {
- for (; *s == *c; s++);
- return s-a;
+ for (a=s; *a == *c; a++);
+ return a-s;
}
for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
- for (; *s && BITOP(byteset, *(unsigned char *)s, &); s++);
- return s-a;
+ for (a=s; *a && BITOP(byteset, *(unsigned char *)a, &); a++);
+ return a-s;
}
<https://git.musl-libc.org/cgit/musl/plain/src/string/strtok.c>
#include <string.h>
char *strtok(char *restrict s, const char *restrict sep)
{
static char *p;
+ return strtok_r(s, sep, &p);
- if (!s && !(s = p)) return NULL;
- s += strspn(s, sep);
- if (!*s) return p = 0;
- p = s + strcspn(s, sep);
- if (*p) *p++ = 0;
- else p = 0;
- return s;
}
<https://git.musl-libc.org/cgit/musl/plain/src/string/strtok_r.c>
#include <string.h>
char *strtok_r(char *restrict s, const char *restrict sep, char **restrict p)
{
if (!s && !(s = *p)) return NULL;
s += strspn(s, sep);
- if (!*s) return *p = 0;
+ if (!*s) return *p = NULL;
*p = s + strcspn(s, sep);
if (**p) *(*p)++ = 0;
- else *p = 0;
+ else *p = NULL;
return s;
}
If you want to go a step further, avoid to build the same byteset twice:
<https://git.musl-libc.org/cgit/musl/plain/src/string/strtok_r.c>
#include <string.h>
char *strtok_r(char *restrict s, const char *restrict sep, char **restrict p)
{
+ size_t byteset[32/sizeof(size_t)] = { 0 };
+
if (!s && !(s = *p)) return NULL;
+ if (!*s) return *p = NULL;
+ if (!*sep) return *p = NULL, *s;
- s += strspn(s, sep);
+ for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
+ for (; *s && BITOP(byteset, *(unsigned char *)s, &); s++);
- if (!*s) return *p = 0;
+ if (!*s) return *p = NULL;
- *p = s + strcspn(s, sep);
- if (**p) *(*p)++ = 0;
- else *p = 0;
- return s;
+ sep = s;
+ for (; *s && !BITOP(byteset, *(unsigned char *)s, &); s++);
+ if (*s) *s++ = 0;
+ else *s = NULL;
+ *p = s;
+ return sep;
}
Stefan
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