libc: Implement strspn (with a test)

libs/libc/include/string.h

@@ -51,6 +51,9 @@ extern "C"
     /* 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);
 
+    /* Returns the length of the initial segment of str which consists entirely of bytes in accept. */
+    size_t strspn(const char* str, const char* accept);
+
     /* 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

@@ -135,6 +135,28 @@ extern "C"
         return s - str;
     }
 
+    size_t strspn(const char* str, const char* accept)
+    {
+        const char* s = str;
+        while (*s)
+        {
+            const char* ap = accept;
+            bool match = false;
+            while (*ap)
+            {
+                if (*s == *ap)
+                {
+                    match = true;
+                    break;
+                }
+                ap++;
+            }
+            if (!match) return s - str;
+            s++;
+        }
+        return s - str;
+    }
+
     char* strcat(char* dest, const char* src)
     {
         size_t dest_len = strlen(dest);

tests/libc/Test.c

@@ -3,6 +3,7 @@
 DEFINE_TEST(strlen);
 DEFINE_TEST(strnlen);
 DEFINE_TEST(strcspn);
+DEFINE_TEST(strspn);
 
 DEFINE_TEST(atoi);
 DEFINE_TEST(atol);
@@ -15,6 +16,7 @@ int main()
     RUN_TEST(strlen);
     RUN_TEST(strnlen);
     RUN_TEST(strcspn);
+    RUN_TEST(strspn);
 
     START_TEST_CASE(stdlib.h);
     RUN_TEST(atoi);

tests/libc/string.c

@@ -61,3 +61,27 @@ DEFINE_TEST(strcspn)
 
     TEST_SUCCESS();
 }
+
+DEFINE_TEST(strspn)
+{
+    START_TEST(strspn);
+
+    const char* str = "This is a test string";
+    const char* accept = "This ";
+
+    size_t len = strspn(str, accept);
+
+    EXPECT_EQ(len, 8);
+
+    str = "WWWWW";
+    len = strspn(str, accept);
+
+    EXPECT_EQ(len, 0);
+
+    str = "This is hi";
+    len = strspn(str, accept);
+
+    EXPECT_EQ(len, 10);
+
+    TEST_SUCCESS();
+}