zrsh.c - libzahl - big integer library
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       ---
       zrsh.c (906B)
       ---
            1 /* See LICENSE file for copyright and license details. */
            2 #include "internals.h"
            3 
            4 
            5 void
            6 zrsh(z_t a, z_t b, size_t bits)
            7 {
            8         size_t i, chars, cbits;
            9 
           10         if (unlikely(!bits)) {
           11                 SET(a, b);
           12                 return;
           13         }
           14 
           15         chars = FLOOR_BITS_TO_CHARS(bits);
           16 
           17         if (unlikely(zzero(b) || chars >= b->used || zbits(b) <= bits)) {
           18                 SET_SIGNUM(a, 0);
           19                 return;
           20         }
           21 
           22         bits = BITS_IN_LAST_CHAR(bits);
           23         cbits = BITS_PER_CHAR - bits;
           24 
           25         if (likely(chars) && likely(a == b)) {
           26                 a->used -= chars;
           27                 zmemmove(a->chars, a->chars + chars, a->used);
           28         } else if (unlikely(a != b)) {
           29                 a->used = b->used - chars;
           30                 ENSURE_SIZE(a, a->used);
           31                 zmemcpy(a->chars, b->chars + chars, a->used);
           32         }
           33 
           34         if (unlikely(bits)) { /* This if statement is very important in C. */
           35                 a->chars[0] >>= bits;
           36                 for (i = 1; i < a->used; i++) {
           37                         a->chars[i - 1] |= a->chars[i] << cbits;
           38                         a->chars[i] >>= bits;
           39                 }
           40                 TRIM_NONZERO(a);
           41         }
           42 
           43         SET_SIGNUM(a, zsignum(b));
           44 }