ref: 7392b1c634dd3137b04ada6f6aa2824f34997ec0
dir: /3rd/mp/mpvecsub.c/
#include "platform.h" // prereq: a >= b, alen >= blen, diff has at least alen digits void mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *diff) { int i, borrow; mpdigit x, y; borrow = 0; for(i = 0; i < blen; i++){ x = *a++; y = *b++; y += borrow; if(y < (mpdigit)borrow) borrow = 1; else borrow = 0; if(x < y) borrow++; *diff++ = x - y; } for(; i < alen; i++){ x = *a++; y = x - borrow; if(y > x) borrow = 1; else borrow = 0; *diff++ = y; } }