// This code is Public Domain. Use, modify, and redistribute at will.
// ----------------------------------------------------------------------------
-size_t strspn( const char * s1, const char * s2 ) { /* TODO */ };
+#include <__size_t.h>
+
+size_t strspn( const char * src_1, const char * src_2 )
+{
+ size_t len = 0;
+ const char * p;
+ while ( src_1[ len ] != '\0' )
+ {
+ p = src_2;
+ while ( *p != '\0' )
+ {
+ if ( *src_1 == *p )
+ {
+ break;
+ }
+ ++p;
+ }
+ if ( *p == '\0' )
+ {
+ return len;
+ }
+ ++len;
+ }
+ return len;
+}