ref: 2d0ede468ddd363243fd31580e3e86c39b51f7be
dir: /sys/src/libmp/power/mpvecsub.s/
#define BDNZ BC 16,0, #define BDNE BC 0,2, /* * mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *diff) * * diff[0:alen-1] = a[0:alen-1] - b[0:blen-1] * * prereq: alen >= blen, diff has room for alen digits * * R3 == a * R4 == alen * R5 == b * R6 == blen * R7 == diff * R8 == temporary * R9 == temporary */ TEXT mpvecsub(SB),$-4 MOVW alen+4(FP),R4 MOVW b+8(FP),R5 MOVW blen+12(FP),R6 MOVW diff+16(FP),R7 SUB R6, R4 /* calculate counter for second loop (alen > blen) */ SUB $4, R3 /* pre decrement for MOVWU's */ SUB $4, R5 /* pre decrement for MOVWU's */ SUBC $4, R7 /* pre decrement for MOVWU's and set carry */ /* skip subraction if b is zero */ CMP R0,R6 BEQ _sub1 /* diff[0:blen-1],borrow = a[0:blen-1] - b[0:blen-1] */ MOVW R6, CTR _subloop1: MOVWU 4(R3), R8 MOVWU 4(R5), R9 SUBE R9, R8, R8 MOVWU R8, 4(R7) BDNZ _subloop1 _sub1: /* skip subtraction if a is zero */ CMP R0, R4 BEQ _subend /* diff[blen:alen-1] = a[blen:alen-1] - 0 + carry */ MOVW R4, CTR _subloop2: MOVWU 4(R3), R8 SUBE R0, R8 MOVWU R8, 4(R7) BDNZ _subloop2 _subend: RETURN