libc: Add strcspn (with a test)

libs/libc/include/string.h

@@ -48,6 +48,9 @@ extern "C"
     /* Concatenates at most max bytes of the string src into dest. */
     char* strncat(char* dest, const char* src, size_t max);
 
+    /* Returns the length of the initial segment of str which consists entirely of bytes not in reject. */
+    size_t strcspn(const char* str, const char* reject);
+
     /* Compares strings a and b. You might prefer to use the safer strncmp function. */
     int strcmp(const char* a, const char* b);
 

libs/libc/src/string.cpp

@@ -119,6 +119,22 @@ extern "C"
         return *(const unsigned char*)a - *(const unsigned char*)b;
     }
 
+    size_t strcspn(const char* str, const char* reject)
+    {
+        const char* s = str;
+        while (*s)
+        {
+            const char* rp = reject;
+            while (*rp)
+            {
+                if (*s == *rp) return s - str;
+                rp++;
+            }
+            s++;
+        }
+        return s - str;
+    }
+
     char* strcat(char* dest, const char* src)
     {
         size_t dest_len = strlen(dest);

tests/libc/Test.c

@@ -2,10 +2,12 @@
 
 DEFINE_TEST(strlen);
 DEFINE_TEST(strnlen);
+DEFINE_TEST(strcspn);
 
 int main()
 {
     START_TEST_CASE(string.h);
     RUN_TEST(strlen);
     RUN_TEST(strnlen);
+    RUN_TEST(strcspn);
 }

tests/libc/string.c

@@ -42,3 +42,22 @@ DEFINE_TEST(strnlen)
 
     TEST_SUCCESS();
 }
+
+DEFINE_TEST(strcspn)
+{
+    START_TEST(strcspn);
+
+    const char* str = "This string has vowels";
+    const char* vowels = "aeiou";
+
+    size_t len = strcspn(str, vowels);
+
+    EXPECT_EQ(len, 2);
+
+    str = "WWWWW";
+    len = strcspn(str, vowels);
+
+    EXPECT_EQ(len, 5);
+
+    TEST_SUCCESS();
+}