fmt: add scn_u32_hex()

sys/fmt/fmt.c

@@ -460,6 +460,30 @@ uint32_t scn_u32_dec(const char *str, size_t n)
     return res;
 }
 
+uint32_t scn_u32_hex(const char *str, size_t n)
+{
+    uint32_t res = 0;
+
+    while (n--) {
+        char c = *str++;
+        if (!_is_digit(c)) {
+            if (_is_upper(c)) {
+                c = _to_lower(c);
+            }
+            if (c == '\0' || c > 'f') {
+                break;
+            }
+            res <<= 4;
+            res |= c - 'a' + 0xa;
+        }
+        else {
+            res <<= 4;
+            res |= c - '0';
+        }
+    }
+    return res;
+}
+
 void print(const char *s, size_t n)
 {
 #ifdef __WITH_AVRLIBC__

sys/include/fmt.h

@@ -376,6 +376,18 @@ size_t fmt_to_lower(char *out, const char *str);
  */
 uint32_t scn_u32_dec(const char *str, size_t n);
 
+/**
+ * @brief Convert hexadecimal characters to uin32_t
+ *
+ * Will convert up to @p n char. Stop at any non-hexadecimal or '\0' character
+ *
+ * @param[in]   str Pointer to tring to read from
+ * @param[in]   n   Maximum number of characters to consider
+ *
+ * @return  converted uint32_t value
+ */
+uint32_t scn_u32_hex(const char *str, size_t n);
+
 /**
  * @brief Print string to stdout
  *

tests/unittests/tests-fmt/tests-fmt.c

@@ -779,6 +779,17 @@ static void test_scn_u32_dec(void)
     TEST_ASSERT_EQUAL_INT(val2, scn_u32_dec(string1, 5));
 }
 
+static void test_scn_u32_hex(void)
+{
+    const char *string1 = "aB12cE4F";
+    uint32_t val1 = 0xab12ce4f;
+    uint32_t val2 = 0xab1;
+
+    TEST_ASSERT_EQUAL_INT(val1, scn_u32_hex(string1, 8));
+    TEST_ASSERT_EQUAL_INT(val2, scn_u32_hex(string1, 3));
+    TEST_ASSERT_EQUAL_INT(val1, scn_u32_hex(string1, 9));
+}
+
 static void test_fmt_lpad(void)
 {
     const char base[] = "abcd";
@@ -840,6 +851,7 @@ Test *tests_fmt_tests(void)
         new_TestFixture(test_fmt_char),
         new_TestFixture(test_fmt_to_lower),
         new_TestFixture(test_scn_u32_dec),
+        new_TestFixture(test_scn_u32_hex),
         new_TestFixture(test_fmt_lpad),
     };