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-rw-r--r--src/string/strspn.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/src/string/strspn.c b/src/string/strspn.c
new file mode 100644
index 00000000..59b063e5
--- /dev/null
+++ b/src/string/strspn.c
@@ -0,0 +1,22 @@
+#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)
+{
+ const unsigned char *s = _s;
+ const unsigned char *c = _c;
+ const unsigned char *a = s;
+ size_t byteset[32/sizeof(size_t)] = { 0 };
+
+ if (!c[0]) return 0;
+ if (!c[1]) {
+ for (; *s == *c; s++);
+ return s-a;
+ }
+
+ for (; *c && BITOP(byteset, *c, |=); c++);
+ for (; *s && BITOP(byteset, *s, &); s++);
+ return s-a;
+}