/* $OpenBSD: impys.S,v 1.8 2002/09/20 19:26:59 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 ;**************************************************************************** ; ;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