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	zsub.c - libzahl - big integer library
	git clone git://git.suckless.org/libzahl
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	zsub.c (1941B)
	---
	1 /* See LICENSE file for copyright and license details. */
	2 #include "internals.h"
	3
	4
	5 static inline void
	6 zsub_impl(z_t a, z_t b, size_t n)
	7 {
	8 zahl_char_t carry = 0, tcarry;
	9 size_t i;
	10
	11 for (i = 0; i < n; i++) {
	12 tcarry = carry ? (a->chars[i] <= b->chars[i]) : (a->char…
	13 a->chars[i] -= b->chars[i];
	14 a->chars[i] -= carry;
	15 carry = tcarry;
	16 }
	17
	18 if (carry) {
	19 while (!a->chars[i])
	20 a->chars[i++] = ZAHL_CHAR_MAX;
	21 if (a->chars[i] == 1)
	22 a->used--;
	23 else
	24 a->chars[i] -= 1;
	25 }
	26 }
	27
	28 static inline void
	29 libzahl_zsub_unsigned(z_t a, z_t b, z_t c)
	30 {
	31 int magcmp;
	32 size_t n;
	33
	34 if (unlikely(zzero(b))) {
	35 zabs(a, c);
	36 zneg(a, a);
	37 return;
	38 } else if (unlikely(zzero(c))) {
	39 zabs(a, b);
	40 return;
	41 }
	42
	43 magcmp = zcmpmag(b, c);
	44 if (unlikely(magcmp <= 0)) {
	45 if (unlikely(magcmp == 0)) {
	46 SET_SIGNUM(a, 0);
	47 return;
	48 }
	49 n = b->used;
	50 if (a == b) {
	51 zset(libzahl_tmp_sub, b);
	52 SET(a, c);
	53 zsub_impl(a, libzahl_tmp_sub, n);
	54 } else {
	55 SET(a, c);
	56 zsub_impl(a, b, n);
	57 }
	58 } else {
	59 n = c->used;
	60 if (unlikely(a == c)) {
	61 zset(libzahl_tmp_sub, c);
	62 SET(a, b);
	63 zsub_impl(a, libzahl_tmp_sub, n);
	64 } else {
	65 SET(a, b);
	66 zsub_impl(a, c, n);
	67 }
	68 }
	69
	70 SET_SIGNUM(a, magcmp);
	71 }
	72
	73 void
	74 zsub_unsigned(z_t a, z_t b, z_t c)
	75 {
	76 libzahl_zsub_unsigned(a, b, c);
	77 }
	78
	79 void
	80 zsub_nonnegative_assign(z_t a, z_t b)
	81 {
	82 if (unlikely(zzero(b)))
	83 zabs(a, a);
	84 else if (unlikely(!zcmpmag(a, b)))
	85 SET_SIGNUM(a, 0);
	86 else
	87 zsub_impl(a, b, b->used);
	88 }
	89
	90 void
	91 zsub_positive_assign(z_t a, z_t b)
	92 {
	93 zsub_impl(a, b, b->used);
	94 }
	95
	96 void
	97 zsub(z_t a, z_t b, z_t c)
	98 {
	99 if (unlikely(zzero(b))) {
	100 zneg(a, c);
	101 } else if (unlikely(zzero(c))) {
	102 SET(a, b);
	103 } else if (unlikely(znegative(b))) {
	104 if (znegative(c)) {
	105 libzahl_zsub_unsigned(a, c, b);
	106 } else {
	107 zadd_unsigned(a, b, c);
	108 SET_SIGNUM(a, -zsignum(a));
	109 }
	110 } else if (znegative(c)) {
	111 zadd_unsigned(a, b, c);
	112 } else {
	113 libzahl_zsub_unsigned(a, b, c);
	114 }
	115 }