* The caller must ensure num_digits >= actual digits in x.

* Leading zeros are added if x has fewer digits than num_digits.

*/

/* Batch divisor: 10^9 for extracting 9 digits at once */

/* Batch divisor for extracting multiple digits at once */

#ifdef MRB_NO_MPZ64BIT

/* 16-bit limbs: 10^4 fits in 16 bits */

#define BATCH_DIVISOR 10000UL

#define BATCH_DIGITS 4

#else

/* 32-bit limbs: 10^9 fits in 32 bits */

#define BATCH_DIVISOR 1000000000UL

#define BATCH_DIGITS 9

#endif

/*

* Divide limb array by 10^9 in place, returning remainder.

* Used for extracting 9 decimal digits at a time.

* Divide limb array by BATCH_DIVISOR in place, returning remainder.

* Used for extracting BATCH_DIGITS decimal digits at a time.

* Compilers optimize constant division to multiplication+shift.

*/

static mp_limb

mpz_set(ctx, tmp, x);

while (pos > 0 && !zero_p(tmp)) {

/* Divide by 10^9 in place, get remainder as 9 digits */

/* Divide by BATCH_DIVISOR in place, get remainder as BATCH_DIGITS digits */

mp_limb batch = mpn_div_batch(tmp->p, tmp->sz);

trim(tmp);

/* Convert remainder (0-999999999) to 9 digits using table lookup */

/* Extract last digit (9th) separately since 9 is odd */

/* Convert remainder to BATCH_DIGITS digits using table lookup */

#if (BATCH_DIGITS % 2) == 1

/* Extract last digit separately since BATCH_DIGITS is odd */

if (pos > 0) {

s[--pos] = '0' + (char)(batch % 10);

batch /= 10;

}

/* Extract remaining 8 digits as 4 pairs using lookup table */

for (int d = 0; d < 4 && pos >= 2; d++) {

#endif

/* Extract remaining digits as pairs using lookup table */

for (int d = 0; d < BATCH_DIGITS / 2 && pos >= 2; d++) {

mp_limb pair = batch % 100;

batch /= 100;

s[--pos] = digit_pairs[pair * 2 + 1];