Merge pull request #6784 from kaspar030/add_fmt_lpad

sys: fmt: add fmt_lpad()

sys/fmt/fmt.c

@@ -243,6 +243,33 @@ size_t fmt_s16_dfp(char *out, int16_t val, unsigned fp_digits)
     return pos;
 }
 
+size_t fmt_lpad(char *out, size_t in_len, size_t pad_len, char pad_char)
+{
+    if (in_len >= pad_len) {
+        return in_len;
+    }
+
+    size_t n = pad_len - in_len;
+
+    if (FMT_USE_MEMMOVE) {
+        memmove(out + n, out, in_len);
+        memset(out, pad_char, n);
+    }
+    else {
+        char *pos = out + pad_len - 1;
+        out += in_len -1;
+
+        while(in_len--) {
+            *pos-- = *out--;
+        }
+
+        while (n--) {
+            *pos-- = pad_char;
+        }
+    }
+    return pad_len;
+}
+
 uint32_t scn_u32_dec(const char *str, size_t n)
 {
     uint32_t res = 0;

sys/include/fmt.h

@@ -41,6 +41,10 @@
 extern "C" {
 #endif
 
+#ifndef FMT_USE_MEMMOVE
+#define FMT_USE_MEMMOVE (1) /**< use memmove() or internal implementation */
+#endif
+
 /**
  * @brief Format a byte value as hex
  *
@@ -294,6 +298,28 @@ void print_u64_dec(uint64_t val);
  */
 void print_str(const char* str);
 
+/**
+ * @brief Pad string to the left
+ *
+ * This function left-pads a given string @p out with @p pad_char
+ *
+ * For example, calling
+ *
+ *     fmt_lpad("abcd", 4, 7, ' ');
+ *
+ * would result in "   abcd".
+ *
+ * @note Caller must ensure @p str can take pad_len characters!
+ *
+ * @param[inout]    str         string to pad
+ * @param[in]       in_len      length of str
+ * @param[in]       pad_len     total length after padding
+ * @param[in]       pad_char    char to use as pad char
+ *
+ * @returns pad_len
+ */
+size_t fmt_lpad(char *str, size_t in_len, size_t pad_len, char pad_char);
+
 #ifdef __cplusplus
 }
 #endif

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

@@ -13,6 +13,7 @@
  */
 #include <errno.h>
 #include <stdint.h>
+#include <string.h>
 
 #include "embUnit/embUnit.h"
 
@@ -275,6 +276,38 @@ static void test_scn_u32_dec(void)
     TEST_ASSERT_EQUAL_INT(val2, scn_u32_dec(string1, 5));
 }
 
+static void test_fmt_lpad(void)
+{
+    const char base[] = "abcd";
+    char string[9] = {0};
+
+    strcpy(string, base);
+
+    fmt_lpad(string, 4, 8, ' ');
+
+    TEST_ASSERT_EQUAL_STRING("    abcd", (char*)string);
+
+    fmt_lpad(string, 0, 0, '1');
+
+    TEST_ASSERT_EQUAL_STRING("    abcd", (char*)string);
+
+    fmt_lpad(string, 4, 0, '2');
+
+    TEST_ASSERT_EQUAL_STRING("    abcd", (char*)string);
+
+    fmt_lpad(string, 0, 4, '3');
+
+    TEST_ASSERT_EQUAL_STRING("3333abcd", (char*)string);
+
+    fmt_lpad(string, 8, 8, '4');
+
+    TEST_ASSERT_EQUAL_STRING("3333abcd", (char*)string);
+
+    fmt_lpad(string, 4, 8, 'x');
+
+    TEST_ASSERT_EQUAL_STRING((char*)string, "xxxx3333");
+}
+
 Test *tests_fmt_tests(void)
 {
     EMB_UNIT_TESTFIXTURES(fixtures) {
@@ -293,6 +326,7 @@ Test *tests_fmt_tests(void)
         new_TestFixture(test_fmt_strlen),
         new_TestFixture(test_fmt_str),
         new_TestFixture(test_scn_u32_dec),
+        new_TestFixture(test_fmt_lpad),
     };
 
     EMB_UNIT_TESTCALLER(fmt_tests, NULL, NULL, fixtures);