diff --git a/sys/fmt/fmt.c b/sys/fmt/fmt.c
index 9c951be387a18f2b518f1d56f3a01de01da7e131..e75c7487a34d36c1a27879e7dc19f944a0f0ff23 100644
--- a/sys/fmt/fmt.c
+++ b/sys/fmt/fmt.c
@@ -263,48 +263,56 @@ size_t fmt_s16_dec(char *out, int16_t val)
return fmt_s32_dec(out, val);
}
-size_t fmt_s16_dfp(char *out, int16_t val, unsigned fp_digits)
+size_t fmt_s16_dfp(char *out, int16_t val, int fp_digits)
{
return fmt_s32_dfp(out, val, fp_digits);
}
-size_t fmt_s32_dfp(char *out, int32_t val, unsigned fp_digits)
+size_t fmt_s32_dfp(char *out, int32_t val, int fp_digits)
{
- assert(fp_digits < TENMAP_SIZE);
+ assert(fp_digits > -(int)TENMAP_SIZE);
- int32_t absolute, divider;
- unsigned div_len, len, pos = 0;
- char tmp[9];
+ unsigned pos = 0;
if (fp_digits == 0) {
- return fmt_s32_dec(out, val);
+ pos = fmt_s32_dec(out, val);
}
- if (val < 0) {
+ else if (fp_digits > 0) {
+ pos = fmt_s32_dec(out, val);
if (out) {
- out[pos++] = '-';
+ memset(&out[pos], '0', fp_digits);
}
- val = -val;
- }
-
- uint32_t e = _tenmap[fp_digits];
- absolute = (val / e);
- divider = val - (absolute * e);
-
- pos += fmt_s32_dec(&out[pos], absolute);
-
- if (!out) {
- return pos + 1 + fp_digits; /* abs len + decimal point + divider */
+ pos += fp_digits;
}
+ else {
+ fp_digits *= -1;
+ uint32_t e = _tenmap[fp_digits];
+ int32_t abs = (val / (int32_t)e);
+ int32_t div = val - (abs * e);
+
+ /* the divisor should never be negative */
+ if (div < 0) {
+ div *= -1;
+ }
+ /* handle special case for negative number with zero as absolute value */
+ if ((abs == 0) && (val < 0)) {
+ if (out) {
+ out[pos] = '-';
+ }
+ pos++;
+ }
- out[pos++] = '.';
- len = pos + fp_digits;
- div_len = fmt_s32_dec(tmp, divider);
-
- while (pos < (len - div_len)) {
- out[pos++] = '0';
- }
- for (size_t i = 0; i < div_len; i++) {
- out[pos++] = tmp[i];
+ if (!out) {
+ /* compensate for the decimal point character... */
+ pos += fmt_s32_dec(NULL, abs) + 1;
+ }
+ else {
+ pos += fmt_s32_dec(&out[pos], abs);
+ out[pos++] = '.';
+ unsigned div_len = fmt_s32_dec(&out[pos], div);
+ fmt_lpad(&out[pos], div_len, (size_t)fp_digits, '0');
+ }
+ pos += fp_digits;
}
return pos;
diff --git a/sys/include/fmt.h b/sys/include/fmt.h
index 3f9e1ea00e829bac43da76c0d5dc58de09229bbb..d88608b2c9266593fbddb0236c781b725ee14d04 100644
--- a/sys/include/fmt.h
+++ b/sys/include/fmt.h
@@ -225,60 +225,43 @@ size_t fmt_s16_dec(char *out, int16_t val);
/**
* @brief Convert 16-bit fixed point number to a decimal string
*
- * The input for this function is a signed 16-bit integer holding the fixed
- * point value as well as an unsigned integer defining the position of the
- * decimal point, so this value defines the number of decimal digits after the
- * decimal point.
- *
- * The resulting string will always be patted with zeros after the decimal point.
- *
- * For example: if @p val is -3548 and @p fp_digits is 2, the resulting string
- * will be "-35.48". For @p val := 12010 and @p fp_digits := 3 the result will
- * be "12.010".
- *
- * Will add a leading "-" if @p val is negative.
- *
- * If @p out is NULL, will only return the number of bytes that would have
- * been written.
- *
- * @pre fp_digits < 8 (TENMAP_SIZE)
+ * See fmt_s32_dfp() for more details
*
* @param[out] out Pointer to the output buffer, or NULL
* @param[in] val Fixed point value
- * @param[in] fp_digits Number of digits after the decimal point
+ * @param[in] fp_digits Number of digits after the decimal point, MUST be
+ * >= -7
*
* @return Length of the resulting string
*/
-size_t fmt_s16_dfp(char *out, int16_t val, unsigned fp_digits);
+size_t fmt_s16_dfp(char *out, int16_t val, int fp_digits);
/**
* @brief Convert 32-bit fixed point number to a decimal string
*
* The input for this function is a signed 32-bit integer holding the fixed
- * point value as well as an unsigned integer defining the position of the
- * decimal point, so this value defines the number of decimal digits after the
- * decimal point.
+ * point value as well as an integer defining the position of the decimal point.
+ * This value is used to shift the decimal point to the right (positive value
+ * of @p fp_digits) or to the left (negative value of @p fp_digits).
*
* Will add a leading "-" if @p val is negative.
*
* The resulting string will always be patted with zeros after the decimal point.
*
- * For example: if @p val is -314159 and @p fp_digits is 5, the resulting string
- * will be "-3.14159". For @p val := 16777215 and @p fp_digits := 6 the result
- * will be "16.777215".
- *
- * If @p out is NULL, will only return the number of bytes that would have
- * been written.
+ * For example: if @p val is -3548 and @p fp_digits is -2, the resulting string
+ * will be "-35.48". The same value for @p val with @p fp_digits of 2 will
+ * result in "-354800".
*
- * @pre fp_digits < 8 (TENMAP_SIZE)
+ * @pre fp_digits > -8 (TENMAP_SIZE)
*
* @param[out] out Pointer to the output buffer, or NULL
* @param[in] val Fixed point value
- * @param[in] fp_digits Number of digits after the decimal point
+ * @param[in] fp_digits Number of digits after the decimal point, MUST be
+ * >= -7
*
* @return Length of the resulting string
*/
-size_t fmt_s32_dfp(char *out, int32_t val, unsigned fp_digits);
+size_t fmt_s32_dfp(char *out, int32_t val, int fp_digits);
/**
* @brief Format float to string