126 lines
2.5 KiB
ArmAsm
126 lines
2.5 KiB
ArmAsm
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/* ------------------------------------------------------------------ */
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/* | Copyright Unpublished, MIPS Computer Systems, Inc. All Rights | */
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/* | Reserved. This software contains proprietary and confidential | */
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/* | information of MIPS and its suppliers. Use, disclosure or | */
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/* | reproduction is prohibited without the prior express written | */
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/* | consent of MIPS. | */
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/* ------------------------------------------------------------------ */
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#ident "$Header"
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/*
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* Copyright 1985 by MIPS Computer Systems, Inc.
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*/
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/* bcmp(s1, s2, n) */
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#include "kxmips.h"
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/*
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* bcmp(src, dst, bcount)
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*
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* MINCMP is minimum number of byte that its worthwhile to try and
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* align cmp into word transactions
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*
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* Calculating MINCMP
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* Overhead =~ 15 instructions => 90 cycles
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* Byte cmp =~ 38 cycles/word
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* Word cmp =~ 17 cycles/word
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* Breakeven =~ 16 bytes
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*/
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#define MINCMP 16
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#define NBPW 4
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LEAF_ENTRY(memcmp)
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xor v0,a0,a1
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blt a2,MINCMP,bytecmp # too short, just byte cmp
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and v0,NBPW-1
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subu t8,zero,a0 # number of bytes til aligned
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bne v0,zero,unalgncmp # src and dst not alignable
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/*
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* src and dst can be simultaneously word aligned
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*/
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and t8,NBPW-1
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subu a2,t8
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beq t8,zero,wordcmp # already aligned
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move v0,v1 # lw[lr] don't clear target reg
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lwr v0,0(a0)
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lwr v1,0(a1)
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addu a0,t8
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addu a1,t8
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bne v0,v1,cmpne
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/*
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* word cmp loop
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*/
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wordcmp:
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and a3,a2,~(NBPW-1)
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subu a2,a3
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beq a3,zero,bytecmp
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addu a3,a0 # src1 endpoint
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1: lw v0,0(a0)
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lw v1,0(a1)
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addu a0,NBPW # 1st BDSLOT
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addu a1,NBPW # 2nd BDSLOT (asm doesn't move)
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bne v0,v1,cmpne
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bne a0,a3,1b # at least one more word
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b bytecmp
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/*
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* deal with simultaneously unalignable cmp by aligning one src
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*/
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unalgncmp:
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subu a3,zero,a1 # calc byte cnt to get src2 aligned
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and a3,NBPW-1
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subu a2,a3
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beq a3,zero,partaligncmp # already aligned
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addu a3,a0 # src1 endpoint
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1: lbu v0,0(a0)
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lbu v1,0(a1)
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addu a0,1
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addu a1,1
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bne v0,v1,cmpne
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bne a0,a3,1b
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/*
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* src unaligned, dst aligned loop
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*/
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partaligncmp:
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and a3,a2,~(NBPW-1)
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subu a2,a3
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beq a3,zero,bytecmp
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addu a3,a0
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1:
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lwr v0,0(a0)
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lwl v0,3(a0)
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lw v1,0(a1)
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addu a0,NBPW
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addu a1,NBPW
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bne v0,v1,cmpne
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bne a0,a3,1b
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/*
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* brute force byte cmp loop
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*/
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bytecmp:
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addu a3,a2,a0 # src1 endpoint; BDSLOT
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ble a2,zero,cmpdone
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1: lbu v0,0(a0)
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lbu v1,0(a1)
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addu a0,1
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addu a1,1
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bne v0,v1,cmpne
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bne a0,a3,1b
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cmpdone:
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move v0,zero
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j ra
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cmpne:
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sltu a2,v1,v0
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bne a2,zero,9f
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li v0,-1
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j ra
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9:
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li v0,1
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j ra
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.end bcmp
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