181 lines
8.2 KiB
NASM
181 lines
8.2 KiB
NASM
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;*****************************************************************************
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;*
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;* Open Watcom Project
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;*
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;* Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
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;*
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;* ========================================================================
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;*
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;* This file contains Original Code and/or Modifications of Original
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;* Code as defined in and that are subject to the Sybase Open Watcom
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;* Public License version 1.0 (the 'License'). You may not use this file
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;* except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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;* ALL TERMS AND CONDITIONS OF THE LICENSE. A copy of the License is
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;* provided with the Original Code and Modifications, and is also
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;* available at www.sybase.com/developer/opensource.
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;*
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;* The Original Code and all software distributed under the License are
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;* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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;* EXPRESS OR IMPLIED, AND SYBASE AND ALL CONTRIBUTORS HEREBY DISCLAIM
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;* ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF
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;* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR
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;* NON-INFRINGEMENT. Please see the License for the specific language
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;* governing rights and limitations under the License.
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;*
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;* ========================================================================
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;*
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;* Description: WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
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;* DESCRIBE IT HERE!
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;*
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;*****************************************************************************
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include mdef.inc
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include struct.inc
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modstart fprem386
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xdefp __fprem_
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;
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; EDX:EAX ECX:EBX
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; void fprem( double x, double modulus, int *quot, double *rem )
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;
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defpe __fprem_
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push EBP ; save BP
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mov EBP,ESP ; get access to parms
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push EDX ; save registers
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push ECX ; ...
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push EBX ; ...
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push EAX ; ...
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mov EAX,8[EBP] ; get argument x
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mov EDX,12[EBP] ; ...
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mov EBX,16[EBP] ; get modulus
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mov ECX,20[EBP] ; ...
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or ECX,ECX ; if modulus is zero
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_if e ; then
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sub EAX,EAX ; - set result to 0
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mov EBX,24[EBP] ; - quot = 0
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mov [EBX],EAX ; - ...
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mov EBX,28[EBP] ; - remainder = 0
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mov [EBX],EAX ; - ...
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mov 4[EBX],EAX ; - ...
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pop EAX ; - restore registers
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pop EBX ; - ...
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pop ECX ; - ...
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pop EDX ; - ...
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pop EBP ; - restore EBP
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ret ; - return
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_endif ; endif
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push ESI ; save ESI
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push EDI ; save EDI
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push EDX ; save sign of operand
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push ECX ; save high part of modulus
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mov ESI,EDX ; get most sig word of op1
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mov EDI,ECX ; get most sig word of op2
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and ESI,7FF00000h ; isolate exponent
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and EDI,7FF00000h ; isolate exponent of modulus
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and EDX,000FFFFFh ; isolate mantissa of op1
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and ECX,000FFFFFh ; isolate mantissa of modulus
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or EDX,00100000h ; set implied 1 bit
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or ECX,00100000h ; ...
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sub ESI,EDI ; calculate difference in exponents
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_if ge ; if operand >= modulus
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sub EDI,EDI ; - set quotient to 0
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_loop ; - loop
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_guess ; - - guess
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cmp ECX,EDX ; - - - The purpose of this guess is to
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_quif ne ; - - - determine if the divisor will subtract
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cmp EBX,EAX ; - - -
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je try ; - - -
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_endguess ; - - endguess
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_if c ; - - if the carry is set (ie the modulus will
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; - - - definitely subtract from the dividend
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; - - - without a borrow
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try:
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sub EAX,EBX ; - - - subtract divisor from dividend
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sbb EDX,ECX ; - - - . . .
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stc ; - - - set carry to indicate that modulus was
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; - - - successfully subtracted from dividend
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_endif ; - - endif
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didnt_go: _rcl EDI,1 ; - - rotate 1 (if carry set) into quotient word
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sub ESI,00100000h ; - - adjust difference in exponents
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jl _done ; - - quit if done
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_shl EAX,1 ; - - shift dividend left
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_rcl EDX,1 ; - - . . .
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cmp EDX,00200000h
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jae try
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; If bit 5 of dividend is set here, we didnt subtract the modulus from the
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; dividend (recall that the divisor has a 1 in the msb -- if we subtracted
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; it from the dividend without a borrow, the dividend would not have a one
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; in its msb to be shifted into bit 5 tested for in the condition above. If
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; we are rotating a bit into bit 5, the dividend is now big enough that we
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; can be sure of subtracting out the divisor without a borrow, as we have
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; shifted it left one digit.
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cmp EDX,00100000h
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_until b ; - until
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cmc ; - flip the carry bit
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jmp short didnt_go ; - continue
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_done: sub ESI,ESI ; - set SI to 0
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; normalize the remainder in AL:BX:CX:DX
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_guess ; - guess: number is zero
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or EAX,EAX ; - - quit if not zero
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_quif ne ; - - ...
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or EDX,EDX ; - - ...
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_quif ne ; - - ...
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_admit ; - admit: not zero
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_loop ; - - loop
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test EDX,00200000h; - - - quit if number is normalized
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_quif ne ; - - - . . .
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_rcl EAX,1 ; - - - shift result left
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_rcl EDX,1
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sub ESI,00100000h; - - - decrement exponent
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_endloop ; - - endloop
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shr EDX,1 ; - - put in correct position
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rcr EAX,1 ; - - . . .
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add ESI,00100000h ; - - increment exponent
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pop ECX ; - - get high part of modulus
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push ECX ; - - save it again
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and ECX,7FF00000h ; - - isolate exponent of modulus
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add ESI,ECX ; - - adjust exponent of result
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_endguess ; - endguess
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_else ; else
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add ESI,EDI ; - restore exponent
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sub EDI,EDI ; - set quotient to 0
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_endif ; endif
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and EDX,000FFFFFh ; keep just the fraction
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add EDX,ESI ; update high order word
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pop ECX ; restore high part of modulus
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pop ESI ; restore sign
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and ESI,080000000h ; isolate sign bit
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or EDX,EDX ; test high word of remainder
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_if ne ; if remainder is non-zero
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or EDX,ESI ; - make remainder same sign as original opnd
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_endif ; endif
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xor ESI,ECX ; calc sign of quotient
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_if s ; if quotient should be negative
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neg EDI ; - negate quotient
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_endif ; endif
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mov ESI,24[EBP] ; get address of quotient
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mov [ESI],EDI ; store quotient
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mov ESI,28[EBP] ; get address of remainder
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mov [ESI],EAX ; store remainder
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mov 4[ESI],EDX ; ...
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pop EDI ; restore EDI
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pop ESI ; restore ESI
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pop EAX ; restore registers
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pop EBX ; ...
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pop ECX ; ...
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pop EDX ; ...
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pop EBP ; restore EBP
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ret ; return
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endproc __fprem_
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endmod
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end
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