358 lines
8.2 KiB
ArmAsm
358 lines
8.2 KiB
ArmAsm
.file "reg_u_sub.S"
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/*
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* reg_u_sub.S
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*
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* Core floating point subtraction routine.
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*
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* Call from C as:
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* void reg_u_sub(FPU_REG *arg1, FPU_REG *arg2, FPU_REG *answ,
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* int control_w)
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*
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*
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* Copyright (C) 1992,1993,1994
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* W. Metzenthen, 22 Parker St, Ormond, Vic 3163,
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* Australia. E-mail billm@vaxc.cc.monash.edu.au
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* All rights reserved.
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*
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* This copyright notice covers the redistribution and use of the
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* FPU emulator developed by W. Metzenthen. It covers only its use
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* in the 386BSD, FreeBSD and NetBSD operating systems. Any other
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* use is not permitted under this copyright.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must include information specifying
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* that source code for the emulator is freely available and include
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* either:
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* a) an offer to provide the source code for a nominal distribution
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* fee, or
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* b) list at least two alternative methods whereby the source
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* can be obtained, e.g. a publically accessible bulletin board
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* and an anonymous ftp site from which the software can be
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* downloaded.
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* 3. All advertising materials specifically mentioning features or use of
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* this emulator must acknowledge that it was developed by W. Metzenthen.
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* 4. The name of W. Metzenthen may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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* AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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* W. METZENTHEN BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*
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* The purpose of this copyright, based upon the Berkeley copyright, is to
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* ensure that the covered software remains freely available to everyone.
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*
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* The software (with necessary differences) is also available, but under
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* the terms of the GNU copyleft, for the Linux operating system and for
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* the djgpp ms-dos extender.
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*
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* W. Metzenthen June 1994.
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*
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*
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* $FreeBSD$
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*
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*/
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/*
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| Kernel subtraction routine reg_u_sub(reg *arg1, reg *arg2, reg *answ).
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| Takes two valid reg f.p. numbers (TW_Valid), which are
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| treated as unsigned numbers,
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| and returns their difference as a TW_Valid or TW_Zero f.p.
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| number.
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| The first number (arg1) must be the larger.
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| The returned number is normalized.
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| Basic checks are performed if PARANOID is defined.
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*/
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#include <gnu/i386/fpemul/fpu_asm.h>
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.text
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ENTRY(reg_u_sub)
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pushl %ebp
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movl %esp,%ebp
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pushl %esi
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pushl %edi
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pushl %ebx
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movl PARAM1,%esi /* source 1 */
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movl PARAM2,%edi /* source 2 */
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#ifdef DENORM_OPERAND
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cmpl EXP_UNDER,EXP(%esi)
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jg xOp1_not_denorm
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call denormal_operand
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orl %eax,%eax
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jnz FPU_Arith_exit
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xOp1_not_denorm:
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cmpl EXP_UNDER,EXP(%edi)
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jg xOp2_not_denorm
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call denormal_operand
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orl %eax,%eax
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jnz FPU_Arith_exit
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xOp2_not_denorm:
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#endif /* DENORM_OPERAND */
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/* xorl %ecx,%ecx */
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movl EXP(%esi),%ecx
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subl EXP(%edi),%ecx /* exp1 - exp2 */
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#ifdef PARANOID
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/* source 2 is always smaller than source 1 */
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/* jc L_bugged */
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js L_bugged_1
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testl $0x80000000,SIGH(%edi) /* The args are assumed to be be normalized */
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je L_bugged_2
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testl $0x80000000,SIGH(%esi)
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je L_bugged_2
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#endif /* PARANOID */
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/*--------------------------------------+
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| Form a register holding the |
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| smaller number |
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+--------------------------------------*/
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movl SIGH(%edi),%eax /* register ms word */
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movl SIGL(%edi),%ebx /* register ls word */
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movl PARAM3,%edi /* destination */
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movl EXP(%esi),%edx
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movl %edx,EXP(%edi) /* Copy exponent to destination */
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movb SIGN(%esi),%dl
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movb %dl,SIGN(%edi) /* Copy the sign from the first arg */
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xorl %edx,%edx /* register extension */
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/*--------------------------------------+
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| Shift the temporary register |
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| right the required number of |
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| places. |
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+--------------------------------------*/
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L_shift_r:
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cmpl $32,%ecx /* shrd only works for 0..31 bits */
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jnc L_more_than_31
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/* less than 32 bits */
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shrd %cl,%ebx,%edx
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shrd %cl,%eax,%ebx
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shr %cl,%eax
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jmp L_shift_done
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L_more_than_31:
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cmpl $64,%ecx
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jnc L_more_than_63
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subb $32,%cl
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jz L_exactly_32
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shrd %cl,%eax,%edx
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shr %cl,%eax
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orl %ebx,%ebx
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jz L_more_31_no_low /* none of the lowest bits is set */
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orl $1,%edx /* record the fact in the extension */
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L_more_31_no_low:
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movl %eax,%ebx
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xorl %eax,%eax
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jmp L_shift_done
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L_exactly_32:
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movl %ebx,%edx
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movl %eax,%ebx
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xorl %eax,%eax
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jmp L_shift_done
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L_more_than_63:
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cmpw $65,%cx
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jnc L_more_than_64
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/* Shift right by 64 bits */
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movl %eax,%edx
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orl %ebx,%ebx
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jz L_more_63_no_low
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orl $1,%edx
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jmp L_more_63_no_low
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L_more_than_64:
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jne L_more_than_65
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/* Shift right by 65 bits */
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/* Carry is clear if we get here */
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movl %eax,%edx
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rcrl %edx
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jnc L_shift_65_nc
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orl $1,%edx
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jmp L_more_63_no_low
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L_shift_65_nc:
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orl %ebx,%ebx
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jz L_more_63_no_low
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orl $1,%edx
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jmp L_more_63_no_low
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L_more_than_65:
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movl $1,%edx /* The shifted nr always at least one '1' */
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L_more_63_no_low:
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xorl %ebx,%ebx
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xorl %eax,%eax
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L_shift_done:
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L_subtr:
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/*------------------------------+
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| Do the subtraction |
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+------------------------------*/
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xorl %ecx,%ecx
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subl %edx,%ecx
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movl %ecx,%edx
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movl SIGL(%esi),%ecx
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sbbl %ebx,%ecx
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movl %ecx,%ebx
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movl SIGH(%esi),%ecx
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sbbl %eax,%ecx
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movl %ecx,%eax
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#ifdef PARANOID
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/* We can never get a borrow */
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jc L_bugged
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#endif /* PARANOID */
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/*--------------------------------------+
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| Normalize the result |
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+--------------------------------------*/
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testl $0x80000000,%eax
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jnz L_round /* no shifting needed */
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orl %eax,%eax
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jnz L_shift_1 /* shift left 1 - 31 bits */
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orl %ebx,%ebx
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jnz L_shift_32 /* shift left 32 - 63 bits */
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/* A rare case, the only one which is non-zero if we got here
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// is: 1000000 .... 0000
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// -0111111 .... 1111 1
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// --------------------
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// 0000000 .... 0000 1 */
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cmpl $0x80000000,%edx
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jnz L_must_be_zero
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/* Shift left 64 bits */
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subl $64,EXP(%edi)
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movl %edx,%eax
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jmp L_store
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L_must_be_zero:
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#ifdef PARANOID
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orl %edx,%edx
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jnz L_bugged_3
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#endif /* PARANOID */
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/* The result is zero */
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movb TW_Zero,TAG(%edi)
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movl $0,EXP(%edi) /* exponent */
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movl $0,SIGL(%edi)
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movl $0,SIGH(%edi)
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jmp L_exit /* Does not underflow */
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L_shift_32:
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movl %ebx,%eax
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movl %edx,%ebx
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movl $0,%edx
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subl $32,EXP(%edi) /* Can get underflow here */
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/* We need to shift left by 1 - 31 bits */
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L_shift_1:
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bsrl %eax,%ecx /* get the required shift in %ecx */
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subl $31,%ecx
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negl %ecx
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shld %cl,%ebx,%eax
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shld %cl,%edx,%ebx
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shl %cl,%edx
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subl %ecx,EXP(%edi) /* Can get underflow here */
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L_round:
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jmp FPU_round /* Round the result */
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#ifdef PARANOID
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L_bugged_1:
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pushl EX_INTERNAL|0x206
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call EXCEPTION
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pop %ebx
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jmp L_exit
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L_bugged_2:
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pushl EX_INTERNAL|0x209
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call EXCEPTION
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pop %ebx
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jmp L_exit
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L_bugged_3:
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pushl EX_INTERNAL|0x210
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call EXCEPTION
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pop %ebx
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jmp L_exit
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L_bugged_4:
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pushl EX_INTERNAL|0x211
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call EXCEPTION
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pop %ebx
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jmp L_exit
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L_bugged:
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pushl EX_INTERNAL|0x212
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call EXCEPTION
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pop %ebx
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jmp L_exit
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#endif /* PARANOID */
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L_store:
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/*------------------------------+
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| Store the result |
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+------------------------------*/
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movl %eax,SIGH(%edi)
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movl %ebx,SIGL(%edi)
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movb TW_Valid,TAG(%edi) /* Set the tags to TW_Valid */
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cmpl EXP_UNDER,EXP(%edi)
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jle L_underflow
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L_exit:
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popl %ebx
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popl %edi
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popl %esi
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leave
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ret
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L_underflow:
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push %edi
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call arith_underflow
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pop %ebx
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jmp L_exit
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