Page 235 - ARM 64 Bit Assembly Language

Integer mathematics 223

440 if (bit->blks[bit->size-1] == 0)
441 bit->blks[bit->size-2] = ((bigchunk)1<<(BITSPERCHUNK-2));
442 /* this could be more efficient. TODO */
443 while (bigint_gt(bit,zero)) {
444 resplusbit = bigint_add(r, bit);
445 if (bigint_ge(num,resplusbit)) {
446 tmp = num;
447 num = bigint_sub(num,resplusbit);
448 bigint_free(tmp);
449 tmp = bigint_shift_right(r,1);
450 bigint_free(r);
451 r = bigint_add(tmp,bit);
452 bigint_free(tmp);
453 } else {
454 tmp=r;
455 r = bigint_shift_right(r,1);
456 bigint_free(tmp);
457 }
458 bigint_free(resplusbit);
459 tmp = bit;
460 bit = bigint_shift_right(bit,2);
461 bigint_free(tmp);
462 }
463 bigint_free(zero);
464 bigint_free(num);
465 bigint_free(bit);
466 return r;
467 }
468
469 /******************************************************************/
470
471 /* shift left by entire chunks */
472 static bigint bigint_shift_left_chunk(bigint l, int chunks) {
473 bigint tmp = bigint_alloc(l->size + chunks);
474 for (int i = -chunks; i < l->size; i++) {
475 if (i < 0)
476 tmp->blks[i+chunks] = 0;
477 else
478 tmp->blks[i+chunks] = l->blks[i];
479 }
480 return tmp;
481 }
482
483 /* shift right by entire chunks */
484 static bigint bigint_shift_right_chunk(bigint l, int chunks) {
485 bigint tmp = bigint_alloc(l->size - chunks);
486 for (int i = 0; i < tmp->size; i++) {
487 if (i<chunks)
488 tmp->blks[i] = 0; // should do sign extend // TODO comment