libtommath/mp_to_radix.c

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#include "tommath_private.h"
#ifdef MP_TO_RADIX_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
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/* reverse an array, used for radix code */
static void s_reverse(char *s, size_t len)
{
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size_t ix = 0, iy = len - 1u;
while (ix < iy) {
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MP_EXCH(char, s[ix], s[iy]);
++ix;
--iy;
}
}
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/* stores a bignum as a ASCII string in a given radix (2..64)
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*
* Stores upto "size - 1" chars and always a NULL byte, puts the number of characters
* written, including the '\0', in "written".
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*/
mp_err mp_to_radix(const mp_int *a, char *str, size_t maxlen, size_t *written, int radix)
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{
size_t digs;
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mp_err err;
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mp_int t;
mp_digit d;
char *_s = str;
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/* check range of radix and size*/
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if (maxlen < 2u) {
return MP_BUF;
}
if ((radix < 2) || (radix > 64)) {
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return MP_VAL;
}
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/* quick out if its zero */
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if (mp_iszero(a)) {
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*str++ = '0';
*str = '\0';
if (written != NULL) {
*written = 2u;
}
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return MP_OKAY;
}
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if ((err = mp_init_copy(&t, a)) != MP_OKAY) {
return err;
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}
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/* if it is negative output a - */
if (mp_isneg(&t)) {
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/* we have to reverse our digits later... but not the - sign!! */
++_s;
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/* store the flag and mark the number as positive */
*str++ = '-';
t.sign = MP_ZPOS;
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/* subtract a char */
--maxlen;
}
digs = 0u;
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while (!mp_iszero(&t)) {
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if (--maxlen < 1u) {
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/* no more room */
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err = MP_BUF;
goto LBL_ERR;
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}
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if ((err = mp_div_d(&t, (mp_digit)radix, &t, &d)) != MP_OKAY) {
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goto LBL_ERR;
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}
*str++ = s_mp_radix_map[d];
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++digs;
}
/* reverse the digits of the string. In this case _s points
* to the first digit [exluding the sign] of the number
*/
s_reverse(_s, digs);
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/* append a NULL so the string is properly terminated */
*str = '\0';
digs++;
if (written != NULL) {
*written = mp_isneg(a) ? (digs + 1u): digs;
}
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LBL_ERR:
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mp_clear(&t);
return err;
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}
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#endif