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->chars[i] < b->chars[i]);
     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 }