libc: minimal: add strspn and strcspn support

These functions are useful for determining prefixes, as with file system
paths.  They are required by littlefs.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>

lib/libc/minimal/CMakeLists.txt

@@ -13,6 +13,7 @@ zephyr_library_sources(
   source/string/strncasecmp.c
   source/string/strstr.c
   source/string/string.c
+  source/string/strspn.c
   source/stdout/prf.c
   source/stdout/stdout_console.c
   source/stdout/sprintf.c

lib/libc/minimal/include/string.h

@@ -31,6 +31,9 @@ extern char  *strncat(char *_MLIBC_RESTRICT d, const char *_MLIBC_RESTRICT s,
 		      size_t n);
 extern char *strstr(const char *s, const char *find);
 
+extern size_t strspn(const char *s, const char *accept);
+extern size_t strcspn(const char *s, const char *reject);
+
 extern int    memcmp(const void *m1, const void *m2, size_t n);
 extern void  *memmove(void *d, const void *s, size_t n);
 extern void  *memcpy(void *_MLIBC_RESTRICT d, const void *_MLIBC_RESTRICT s,

lib/libc/minimal/source/string/strspn.c

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2019 Peter Bigot Consulting, LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <string.h>
+#include <string.h>
+
+size_t strspn(const char *s,
+	      const char *accept)
+{
+	const char *ins = s;
+
+	while ((*s != '\0') && (strchr(accept, *s) != NULL)) {
+		++s;
+	}
+
+	return s - ins;
+}
+
+size_t strcspn(const char *s,
+	       const char *reject)
+{
+	const char *ins = s;
+
+	while ((*s != '\0') && (strchr(reject, *s) == NULL)) {
+		++s;
+	}
+
+	return s - ins;
+}

tests/lib/c_lib/src/main.c

@@ -249,6 +249,30 @@ void test_strchr(void)
 
 }
 
+/**
+ *
+ * @brief Test string prefix match functions
+ *
+ */
+
+void test_strxspn(void)
+{
+	const char *empty = "";
+	const char *cset = "abc";
+
+	zassert_true(strspn("", empty) == 0U, "strspn empty empty");
+	zassert_true(strcspn("", empty) == 0U, "strcspn empty empty");
+
+	zassert_true(strspn("abde", cset) == 2U, "strspn match");
+	zassert_true(strcspn("abde", cset) == 0U, "strcspn nomatch");
+
+	zassert_true(strspn("da", cset) == 0U, "strspn nomatch");
+	zassert_true(strcspn("da", cset) == 1U, "strcspn match");
+
+	zassert_true(strspn("abac", cset) == 4U, "strspn all");
+	zassert_true(strcspn("defg", cset) == 4U, "strcspn all");
+}
+
 /**
  *
  * @brief Test memory comparison function
@@ -310,6 +334,7 @@ void test_main(void)
 			 ztest_unit_test(test_memset),
 			 ztest_unit_test(test_strlen),
 			 ztest_unit_test(test_strcmp),
+			 ztest_unit_test(test_strxspn),
 			 ztest_unit_test(test_bsearch)
 			 );
 	ztest_run_test_suite(test_c_lib);