1 files changed, 20 insertions, 0 deletions
diff --git a/na/lib/string/strcspn.c b/na/lib/string/strcspn.c
new file mode 100644
index 0000000..ba55fe6
--- /dev/null
+++ b/na/lib/string/strcspn.c
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: MIT */
+/* Derived from musl libc (Copyright © 2005-2020 Rich Felker, et al.) */
+
+#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)
+{
+	const char *a = s;
+	size_t byteset[32/sizeof(size_t)];
+
+	if (!c[0] || !c[1]) return __strchrnul(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;
+}