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274 lines
6.0 KiB
274 lines
6.0 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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.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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| Copyright (C) 1992,1993,1995,1997 | |
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| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia | |
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| E-mail billm@suburbia.net | |
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| | |
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| Call from C as: | |
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| int FPU_u_sub(FPU_REG *arg1, FPU_REG *arg2, FPU_REG *answ, | |
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| int control_w) | |
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| Return value is the tag of the answer, or-ed with FPU_Exception if | |
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| one was raised, or -1 on internal error. | |
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| | |
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+---------------------------------------------------------------------------*/ |
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/* |
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| Kernel subtraction routine FPU_u_sub(reg *arg1, reg *arg2, reg *answ). |
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| Takes two valid reg f.p. numbers (TAG_Valid), which are |
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| treated as unsigned numbers, |
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| and returns their difference as a TAG_Valid or TAG_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 "exception.h" |
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#include "fpu_emu.h" |
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#include "control_w.h" |
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.text |
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SYM_FUNC_START(FPU_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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movl PARAM6,%ecx |
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subl PARAM7,%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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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 PARAM6,%edx |
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movw %dx,EXP(%edi) /* Copy exponent to destination */ |
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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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cmpw $32,%cx /* 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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cmpw $64,%cx |
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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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/* |
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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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*/ |
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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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subw $64,EXP(%edi) |
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xchg %edx,%eax |
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jmp fpu_reg_round |
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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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movw $0,EXP(%edi) /* exponent */ |
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movl $0,SIGL(%edi) |
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movl $0,SIGH(%edi) |
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movl TAG_Zero,%eax |
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jmp L_exit |
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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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subw $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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subw %cx,EXP(%edi) /* Can get underflow here */ |
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L_round: |
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jmp fpu_reg_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_error_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_error_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_error_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_error_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_error_exit |
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L_error_exit: |
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movl $-1,%eax |
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#endif /* PARANOID */ |
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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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SYM_FUNC_END(FPU_u_sub)
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