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/* $OpenBSD: impys.S,v 1.7 2002/05/07 22:19:30 mickey Exp $ */
/*
(c) Copyright 1986 HEWLETT-PACKARD COMPANY
To anyone who acknowledges that this file is provided "AS IS"
without any express or implied warranty:
permission to use, copy, modify, and distribute this file
for any purpose is hereby granted without fee, provided that
the above copyright notice and this notice appears in all
copies, and that the name of Hewlett-Packard Company not be
used in advertising or publicity pertaining to distribution
of the software without specific, written prior permission.
Hewlett-Packard Company makes no representations about the
suitability of this software for any purpose.
*/
/* @(#)impys.s: Revision: 1.11.88.1 Date: 93/12/07 15:06:28 */
#include <machine/asm.h>
;****************************************************************************
;
;Implement an integer multiply routine for 32-bit operands and 64-bit product
;with operand values of zero (multiplicand only) and -2**31 treated specially.
;The algorithm uses the absolute value of the multiplier, four bits at a time,
;from right to left, to generate partial product. Execution speed is more
;important than program size in this implementation.
;
;****************************************************************************
;
; Definitions - General registers
;
gr0 .equ 0 ; General register zero
pu .equ 3 ; upper part of product
pl .equ 4 ; lower part of product
op2 .equ 4 ; multiplier
op1 .equ 5 ; multiplicand
cnt .equ 6 ; count in multiply
brindex .equ 7 ; index into the br. table
sign .equ 8 ; sign of product
pc .equ 9 ; carry bit of product, = 00...01
pm .equ 10 ; value of -1 used in shifting
;*****************************************************************************
.text
LEAF_ENTRY(impys)
stws,ma pu,4(sp) ; save registers on stack
stws,ma pl,4(sp) ; save registers on stack
stws,ma op1,4(sp) ; save registers on stack
stws,ma cnt,4(sp) ; save registers on stack
stws,ma brindex,4(sp) ; save registers on stack
stws,ma sign,4(sp) ; save registers on stack
stws,ma pc,4(sp) ; save registers on stack
stws,ma pm,4(sp) ; save registers on stack
;
; Start multiply process
;
ldws 0(arg1),op2 ; get multiplier
ldws 0(arg0),op1 ; get multiplicand
addi -1,gr0,pm ; initialize pm to 111...1
comb,< op2,gr0,mpyb ; br. if multiplier < 0
xor op2,op1,sign ; sign(0) = sign of product
mpy1 comb,< op1,gr0,mpya ; br. if multiplicand < 0
addi 0,gr0,pu ; clear product
addib,= 0,op1,fini0 ; op1 = 0, product = 0
mpy2 addi 1,gr0,pc ; initialize pc to 00...01
movib,tr 8,cnt,mloop ; set count for mpy loop
extru op2,31,4,brindex ; 4 bits as index into table
;
.align 8
;
b sh4c ; br. if sign overflow
sh4n shd pu,pl,4,pl ; shift product right 4 bits
addib,<= -1,cnt,mulend ; reduce count by 1, exit if
extru pu,27,28,pu ; <= zero
;
mloop blr brindex,gr0 ; br. into table
; entries of 2 words
extru op2,27,4,brindex ; next 4 bits into index
;
;
; branch table for the multiplication process with four multiplier bits
;
mtable ; two words per entry
;
; ---- bits = 0000 ---- shift product 4 bits -------------------------------
;
b sh4n+4 ; just shift partial
shd pu,pl,4,pl ; product right 4 bits
;
; ---- bits = 0001 ---- add op1, then shift 4 bits
;
addb,tr op1,pu,sh4n+4 ; add op1 to product, to shift
shd pu,pl,4,pl ; product right 4 bits
;
; ---- bits = 0010 ---- add op1, add op1, then shift 4 bits
;
addb,tr op1,pu,sh4n ; add 2*op1, to shift
addb,uv op1,pu,sh4c ; product right 4 bits
;
; ---- bits = 0011 ---- add op1, add 2*op1, shift 4 bits
;
addb,tr op1,pu,sh4n-4 ; add op1 & 2*op1, shift
sh1add,nsv op1,pu,pu ; product right 4 bits
;
; ---- bits = 0100 ---- shift 2, add op1, shift 2
;
b sh2sa
shd pu,pl,2,pl ; shift product 2 bits
;
; ---- bits = 0101 ---- add op1, shift 2, add op1, and shift 2 again
;
addb,tr op1,pu,sh2us ; add op1 to product
shd pu,pl,2,pl ; shift 2 bits
;
; ---- bits = 0110 ---- add op1, add op1, shift 2, add op1, and shift 2 again
;
addb,tr op1,pu,sh2c ; add 2*op1, to shift 2 bits
addb,nuv op1,pu,sh2us ; br. if not overflow
;
; ---- bits = 0111 ---- subtract op1, shift 3, add op1, and shift 1
;
b sh3s
sub pu,op1,pu ; subtract op1, br. to sh3s
;
; ---- bits = 1000 ---- shift 3, add op1, shift 1
;
b sh3sa
shd pu,pl,3,pl ; shift product right 3 bits
;
; ---- bits = 1001 ---- add op1, shift 3, add op1, shift 1
;
addb,tr op1,pu,sh3us ; add op1, to shift 3, add op1,
shd pu,pl,3,pl ; and shift 1
;
; ---- bits = 1010 ---- add op1, add op1, shift 3, add op1, shift 1
;
addb,tr op1,pu,sh3c ; add 2*op1, to shift 3 bits
addb,nuv op1,pu,sh3us ; br. if no overflow
;
; ---- bits = 1011 ---- add -op1, shift 2, add -op1, shift 2, inc. next index
;
addib,tr 1,brindex,sh2s ; add 1 to index, subtract op1,
sub pu,op1,pu ; shift 2 with minus sign
;
; ---- bits = 1100 ---- shift 2, subtract op1, shift 2, increment next index
;
addib,tr 1,brindex,sh2sb ; add 1 to index, to shift
shd pu,pl,2,pl ; shift right 2 bits signed
;
; ---- bits = 1101 ---- add op1, shift 2, add -op1, shift 2
;
addb,tr op1,pu,sh2ns ; add op1, to shift 2
shd pu,pl,2,pl ; right 2 unsigned, etc.
;
; ---- bits = 1110 ---- shift 1 signed, add -op1, shift 3 signed
;
addib,tr 1,brindex,sh1sa ; add 1 to index, to shift
shd pu,pl,1,pl ; shift 1 bit
;
; ---- bits = 1111 ---- add -op1, shift 4 signed
;
addib,tr 1,brindex,sh4s ; add 1 to index, subtract op1,
sub pu,op1,pu ; to shift 4 signed
;
; ---- bits = 10000 ---- shift 4 signed
;
addib,tr 1,brindex,sh4s+4 ; add 1 to index
shd pu,pl,4,pl ; shift 4 signed
;
; ---- end of table ---------------------------------------------------------
;
sh4s shd pu,pl,4,pl
addib,tr -1,cnt,mloop ; loop (count > 0 always here)
shd pm,pu,4,pu ; shift 4, minus signed
;
sh4c addib,> -1,cnt,mloop ; decrement count, loop if > 0
shd pc,pu,4,pu ; shift 4 with overflow
b signs ; end of multiply
bb,>=,n sign,0,fini ; test sign of procduct
;
mpyb add,= op2,op2,gr0 ; if <> 0, back to main sect.
b mpy1
sub 0,op2,op2 ; op2 = |multiplier|
add,>= op1,gr0,gr0 ; if op1 < 0, invert sign,
xor pm,sign,sign ; for correct result
;
; special case for multiplier = -2**31, op1 = signed multiplicand
; or multiplicand = -2**31, op1 = signed multiplier
;
shd op1,0,1,pl ; shift op1 left 31 bits
mmax extrs op1,30,31,pu
b signs ; negate product (if needed)
bb,>=,n sign,0,fini ; test sign of product
;
mpya add,= op1,op1,gr0 ; op1 = -2**31, special case
b mpy2
sub 0,op1,op1 ; op1 = |multiplicand|
add,>= op2,gr0,gr0 ; if op2 < 0, invert sign,
xor pm,sign,sign ; for correct result
movb,tr op2,op1,mmax ; use op2 as multiplicand
shd op1,0,1,pl ; shift it left 31 bits
;
sh3c shd pu,pl,3,pl ; shift product 3 bits
shd pc,pu,3,pu ; shift 3 signed
addb,tr op1,pu,sh1 ; add op1, to shift 1 bit
shd pu,pl,1,pl
;
sh3us extru pu,28,29,pu ; shift 3 unsigned
addb,tr op1,pu,sh1 ; add op1, to shift 1 bit
shd pu,pl,1,pl
;
sh3sa extrs pu,28,29,pu ; shift 3 signed
addb,tr op1,pu,sh1 ; add op1, to shift 1 bit
shd pu,pl,1,pl
;
sh3s shd pu,pl,3,pl ; shift 3 minus signed
shd pm,pu,3,pu
addb,tr op1,pu,sh1 ; add op1, to shift 1 bit
shd pu,pl,1,pl
;
sh1 addib,> -1,cnt,mloop ; loop if count > 0
extru pu,30,31,pu
b signs ; end of multiply
bb,>=,n sign,0,fini ; test sign of product
;
sh2ns addib,tr 1,brindex,sh2sb+4 ; increment index
extru pu,29,30,pu ; shift unsigned
;
sh2s shd pu,pl,2,pl ; shift with minus sign
shd pm,pu,2,pu ;
sub pu,op1,pu ; subtract op1
shd pu,pl,2,pl ; shift with minus sign
addib,tr -1,cnt,mloop ; decrement count, loop
shd pm,pu,2,pu ; shift with minus sign
; count never reaches 0 here
;
sh2sb extrs pu,29,30,pu ; shift 2 signed
sub pu,op1,pu ; subtract op1 from product
shd pu,pl,2,pl ; shift with minus sign
addib,tr -1,cnt,mloop ; decrement count, loop
shd pm,pu,2,pu ; shift with minus sign
; count never reaches 0 here
;
sh1sa extrs pu,30,31,pu ; signed
sub pu,op1,pu ; subtract op1 from product
shd pu,pl,3,pl ; shift 3 with minus sign
addib,tr -1,cnt,mloop ; dec. count, to loop
shd pm,pu,3,pu ; count never reaches 0 here
;
fini0 movib,tr,n 0,pl,fini ; product = 0 as op1 = 0
;
sh2us extru pu,29,30,pu ; shift 2 unsigned
addb,tr op1,pu,sh2a ; add op1
shd pu,pl,2,pl ; shift 2 bits
;
sh2c shd pu,pl,2,pl
shd pc,pu,2,pu ; shift with carry
addb,tr op1,pu,sh2a ; add op1 to product
shd pu,pl,2,pl ; br. to sh2 to shift pu
;
sh2sa extrs pu,29,30,pu ; shift with sign
addb,tr op1,pu,sh2a ; add op1 to product
shd pu,pl,2,pl ; br. to sh2 to shift pu
;
sh2a addib,> -1,cnt,mloop ; loop if count > 0
extru pu,29,30,pu
;
mulend bb,>=,n sign,0,fini ; test sign of product
signs sub 0,pl,pl ; negate product if sign
subb 0,pu,pu ; is negative
;
; finish
;
fini stws pu,0(arg2) ; save high part of result
stws pl,4(arg2) ; save low part of result
ldws,mb -4(sp),pm ; restore registers
ldws,mb -4(sp),pc ; restore registers
ldws,mb -4(sp),sign ; restore registers
ldws,mb -4(sp),brindex ; restore registers
ldws,mb -4(sp),cnt ; restore registers
ldws,mb -4(sp),op1 ; restore registers
ldws,mb -4(sp),pl ; restore registers
bv 0(rp) ; return
ldws,mb -4(sp),pu ; restore registers
EXIT(imyps)
.end
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