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474 lines
12 KiB
474 lines
12 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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.file "reg_u_div.S" |
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/*---------------------------------------------------------------------------+ |
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| reg_u_div.S | |
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| | |
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| Divide one FPU_REG by another and put the result in a destination FPU_REG.| |
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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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| | |
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+---------------------------------------------------------------------------*/ |
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/*---------------------------------------------------------------------------+ |
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| Call from C as: | |
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| int FPU_u_div(FPU_REG *a, FPU_REG *b, FPU_REG *dest, | |
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| unsigned int control_word, char *sign) | |
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| | |
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| Does not compute the destination exponent, but does adjust it. | |
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| | |
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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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#include "exception.h" |
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#include "fpu_emu.h" |
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#include "control_w.h" |
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/* #define dSIGL(x) (x) */ |
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/* #define dSIGH(x) 4(x) */ |
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#ifndef NON_REENTRANT_FPU |
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/* |
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Local storage on the stack: |
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Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0 |
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Overflow flag: ovfl_flag |
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*/ |
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#define FPU_accum_3 -4(%ebp) |
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#define FPU_accum_2 -8(%ebp) |
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#define FPU_accum_1 -12(%ebp) |
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#define FPU_accum_0 -16(%ebp) |
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#define FPU_result_1 -20(%ebp) |
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#define FPU_result_2 -24(%ebp) |
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#define FPU_ovfl_flag -28(%ebp) |
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#else |
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.data |
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/* |
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Local storage in a static area: |
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Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0 |
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Overflow flag: ovfl_flag |
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*/ |
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.align 4,0 |
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FPU_accum_3: |
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.long 0 |
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FPU_accum_2: |
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.long 0 |
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FPU_accum_1: |
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.long 0 |
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FPU_accum_0: |
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.long 0 |
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FPU_result_1: |
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.long 0 |
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FPU_result_2: |
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.long 0 |
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FPU_ovfl_flag: |
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.byte 0 |
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#endif /* NON_REENTRANT_FPU */ |
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#define REGA PARAM1 |
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#define REGB PARAM2 |
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#define DEST PARAM3 |
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.text |
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SYM_FUNC_START(FPU_u_div) |
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pushl %ebp |
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movl %esp,%ebp |
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#ifndef NON_REENTRANT_FPU |
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subl $28,%esp |
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#endif /* NON_REENTRANT_FPU */ |
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pushl %esi |
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pushl %edi |
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pushl %ebx |
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movl REGA,%esi |
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movl REGB,%ebx |
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movl DEST,%edi |
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movswl EXP(%esi),%edx |
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movswl EXP(%ebx),%eax |
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subl %eax,%edx |
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addl EXP_BIAS,%edx |
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/* A denormal and a large number can cause an exponent underflow */ |
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cmpl EXP_WAY_UNDER,%edx |
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jg xExp_not_underflow |
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/* Set to a really low value allow correct handling */ |
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movl EXP_WAY_UNDER,%edx |
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xExp_not_underflow: |
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movw %dx,EXP(%edi) |
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#ifdef PARANOID |
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/* testl $0x80000000, SIGH(%esi) // Dividend */ |
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/* je L_bugged */ |
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testl $0x80000000, SIGH(%ebx) /* Divisor */ |
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je L_bugged |
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#endif /* PARANOID */ |
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/* Check if the divisor can be treated as having just 32 bits */ |
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cmpl $0,SIGL(%ebx) |
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jnz L_Full_Division /* Can't do a quick divide */ |
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/* We should be able to zip through the division here */ |
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movl SIGH(%ebx),%ecx /* The divisor */ |
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movl SIGH(%esi),%edx /* Dividend */ |
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movl SIGL(%esi),%eax /* Dividend */ |
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cmpl %ecx,%edx |
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setaeb FPU_ovfl_flag /* Keep a record */ |
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jb L_no_adjust |
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subl %ecx,%edx /* Prevent the overflow */ |
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L_no_adjust: |
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/* Divide the 64 bit number by the 32 bit denominator */ |
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divl %ecx |
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movl %eax,FPU_result_2 |
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/* Work on the remainder of the first division */ |
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xorl %eax,%eax |
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divl %ecx |
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movl %eax,FPU_result_1 |
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/* Work on the remainder of the 64 bit division */ |
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xorl %eax,%eax |
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divl %ecx |
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testb $255,FPU_ovfl_flag /* was the num > denom ? */ |
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je L_no_overflow |
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/* Do the shifting here */ |
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/* increase the exponent */ |
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incw EXP(%edi) |
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/* shift the mantissa right one bit */ |
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stc /* To set the ms bit */ |
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rcrl FPU_result_2 |
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rcrl FPU_result_1 |
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rcrl %eax |
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L_no_overflow: |
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jmp LRound_precision /* Do the rounding as required */ |
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/*---------------------------------------------------------------------------+ |
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| Divide: Return arg1/arg2 to arg3. | |
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| | |
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| This routine does not use the exponents of arg1 and arg2, but does | |
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| adjust the exponent of arg3. | |
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| | |
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| The maximum returned value is (ignoring exponents) | |
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| .ffffffff ffffffff | |
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| ------------------ = 1.ffffffff fffffffe | |
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| .80000000 00000000 | |
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| and the minimum is | |
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| .80000000 00000000 | |
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| ------------------ = .80000000 00000001 (rounded) | |
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| .ffffffff ffffffff | |
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| | |
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+---------------------------------------------------------------------------*/ |
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L_Full_Division: |
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/* Save extended dividend in local register */ |
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movl SIGL(%esi),%eax |
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movl %eax,FPU_accum_2 |
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movl SIGH(%esi),%eax |
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movl %eax,FPU_accum_3 |
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xorl %eax,%eax |
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movl %eax,FPU_accum_1 /* zero the extension */ |
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movl %eax,FPU_accum_0 /* zero the extension */ |
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movl SIGL(%esi),%eax /* Get the current num */ |
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movl SIGH(%esi),%edx |
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/*----------------------------------------------------------------------*/ |
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/* Initialization done. |
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Do the first 32 bits. */ |
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movb $0,FPU_ovfl_flag |
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cmpl SIGH(%ebx),%edx /* Test for imminent overflow */ |
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jb LLess_than_1 |
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ja LGreater_than_1 |
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cmpl SIGL(%ebx),%eax |
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jb LLess_than_1 |
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LGreater_than_1: |
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/* The dividend is greater or equal, would cause overflow */ |
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setaeb FPU_ovfl_flag /* Keep a record */ |
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subl SIGL(%ebx),%eax |
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sbbl SIGH(%ebx),%edx /* Prevent the overflow */ |
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movl %eax,FPU_accum_2 |
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movl %edx,FPU_accum_3 |
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LLess_than_1: |
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/* At this point, we have a dividend < divisor, with a record of |
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adjustment in FPU_ovfl_flag */ |
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/* We will divide by a number which is too large */ |
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movl SIGH(%ebx),%ecx |
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addl $1,%ecx |
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jnc LFirst_div_not_1 |
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/* here we need to divide by 100000000h, |
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i.e., no division at all.. */ |
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mov %edx,%eax |
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jmp LFirst_div_done |
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LFirst_div_not_1: |
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divl %ecx /* Divide the numerator by the augmented |
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denom ms dw */ |
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LFirst_div_done: |
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movl %eax,FPU_result_2 /* Put the result in the answer */ |
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mull SIGH(%ebx) /* mul by the ms dw of the denom */ |
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subl %eax,FPU_accum_2 /* Subtract from the num local reg */ |
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sbbl %edx,FPU_accum_3 |
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movl FPU_result_2,%eax /* Get the result back */ |
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mull SIGL(%ebx) /* now mul the ls dw of the denom */ |
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subl %eax,FPU_accum_1 /* Subtract from the num local reg */ |
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sbbl %edx,FPU_accum_2 |
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sbbl $0,FPU_accum_3 |
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je LDo_2nd_32_bits /* Must check for non-zero result here */ |
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#ifdef PARANOID |
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jb L_bugged_1 |
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#endif /* PARANOID */ |
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/* need to subtract another once of the denom */ |
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incl FPU_result_2 /* Correct the answer */ |
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movl SIGL(%ebx),%eax |
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movl SIGH(%ebx),%edx |
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subl %eax,FPU_accum_1 /* Subtract from the num local reg */ |
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sbbl %edx,FPU_accum_2 |
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#ifdef PARANOID |
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sbbl $0,FPU_accum_3 |
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jne L_bugged_1 /* Must check for non-zero result here */ |
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#endif /* PARANOID */ |
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/*----------------------------------------------------------------------*/ |
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/* Half of the main problem is done, there is just a reduced numerator |
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to handle now. |
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Work with the second 32 bits, FPU_accum_0 not used from now on */ |
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LDo_2nd_32_bits: |
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movl FPU_accum_2,%edx /* get the reduced num */ |
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movl FPU_accum_1,%eax |
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/* need to check for possible subsequent overflow */ |
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cmpl SIGH(%ebx),%edx |
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jb LDo_2nd_div |
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ja LPrevent_2nd_overflow |
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cmpl SIGL(%ebx),%eax |
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jb LDo_2nd_div |
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LPrevent_2nd_overflow: |
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/* The numerator is greater or equal, would cause overflow */ |
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/* prevent overflow */ |
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subl SIGL(%ebx),%eax |
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sbbl SIGH(%ebx),%edx |
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movl %edx,FPU_accum_2 |
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movl %eax,FPU_accum_1 |
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incl FPU_result_2 /* Reflect the subtraction in the answer */ |
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#ifdef PARANOID |
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je L_bugged_2 /* Can't bump the result to 1.0 */ |
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#endif /* PARANOID */ |
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LDo_2nd_div: |
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cmpl $0,%ecx /* augmented denom msw */ |
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jnz LSecond_div_not_1 |
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/* %ecx == 0, we are dividing by 1.0 */ |
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mov %edx,%eax |
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jmp LSecond_div_done |
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LSecond_div_not_1: |
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divl %ecx /* Divide the numerator by the denom ms dw */ |
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LSecond_div_done: |
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movl %eax,FPU_result_1 /* Put the result in the answer */ |
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mull SIGH(%ebx) /* mul by the ms dw of the denom */ |
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subl %eax,FPU_accum_1 /* Subtract from the num local reg */ |
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sbbl %edx,FPU_accum_2 |
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#ifdef PARANOID |
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jc L_bugged_2 |
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#endif /* PARANOID */ |
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movl FPU_result_1,%eax /* Get the result back */ |
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mull SIGL(%ebx) /* now mul the ls dw of the denom */ |
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subl %eax,FPU_accum_0 /* Subtract from the num local reg */ |
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sbbl %edx,FPU_accum_1 /* Subtract from the num local reg */ |
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sbbl $0,FPU_accum_2 |
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#ifdef PARANOID |
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jc L_bugged_2 |
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#endif /* PARANOID */ |
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jz LDo_3rd_32_bits |
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#ifdef PARANOID |
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cmpl $1,FPU_accum_2 |
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jne L_bugged_2 |
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#endif /* PARANOID */ |
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/* need to subtract another once of the denom */ |
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movl SIGL(%ebx),%eax |
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movl SIGH(%ebx),%edx |
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subl %eax,FPU_accum_0 /* Subtract from the num local reg */ |
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sbbl %edx,FPU_accum_1 |
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sbbl $0,FPU_accum_2 |
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#ifdef PARANOID |
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jc L_bugged_2 |
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jne L_bugged_2 |
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#endif /* PARANOID */ |
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addl $1,FPU_result_1 /* Correct the answer */ |
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adcl $0,FPU_result_2 |
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#ifdef PARANOID |
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jc L_bugged_2 /* Must check for non-zero result here */ |
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#endif /* PARANOID */ |
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/*----------------------------------------------------------------------*/ |
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/* The division is essentially finished here, we just need to perform |
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tidying operations. |
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Deal with the 3rd 32 bits */ |
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LDo_3rd_32_bits: |
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movl FPU_accum_1,%edx /* get the reduced num */ |
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movl FPU_accum_0,%eax |
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/* need to check for possible subsequent overflow */ |
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cmpl SIGH(%ebx),%edx /* denom */ |
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jb LRound_prep |
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ja LPrevent_3rd_overflow |
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cmpl SIGL(%ebx),%eax /* denom */ |
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jb LRound_prep |
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LPrevent_3rd_overflow: |
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/* prevent overflow */ |
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subl SIGL(%ebx),%eax |
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sbbl SIGH(%ebx),%edx |
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movl %edx,FPU_accum_1 |
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movl %eax,FPU_accum_0 |
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addl $1,FPU_result_1 /* Reflect the subtraction in the answer */ |
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adcl $0,FPU_result_2 |
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jne LRound_prep |
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jnc LRound_prep |
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/* This is a tricky spot, there is an overflow of the answer */ |
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movb $255,FPU_ovfl_flag /* Overflow -> 1.000 */ |
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LRound_prep: |
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/* |
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* Prepare for rounding. |
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* To test for rounding, we just need to compare 2*accum with the |
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* denom. |
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*/ |
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movl FPU_accum_0,%ecx |
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movl FPU_accum_1,%edx |
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movl %ecx,%eax |
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orl %edx,%eax |
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jz LRound_ovfl /* The accumulator contains zero. */ |
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/* Multiply by 2 */ |
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clc |
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rcll $1,%ecx |
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rcll $1,%edx |
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jc LRound_large /* No need to compare, denom smaller */ |
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subl SIGL(%ebx),%ecx |
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sbbl SIGH(%ebx),%edx |
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jnc LRound_not_small |
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movl $0x70000000,%eax /* Denom was larger */ |
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jmp LRound_ovfl |
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LRound_not_small: |
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jnz LRound_large |
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movl $0x80000000,%eax /* Remainder was exactly 1/2 denom */ |
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jmp LRound_ovfl |
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LRound_large: |
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movl $0xff000000,%eax /* Denom was smaller */ |
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LRound_ovfl: |
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/* We are now ready to deal with rounding, but first we must get |
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the bits properly aligned */ |
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testb $255,FPU_ovfl_flag /* was the num > denom ? */ |
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je LRound_precision |
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incw EXP(%edi) |
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/* shift the mantissa right one bit */ |
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stc /* Will set the ms bit */ |
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rcrl FPU_result_2 |
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rcrl FPU_result_1 |
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rcrl %eax |
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/* Round the result as required */ |
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LRound_precision: |
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decw EXP(%edi) /* binary point between 1st & 2nd bits */ |
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movl %eax,%edx |
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movl FPU_result_1,%ebx |
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movl FPU_result_2,%eax |
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jmp fpu_reg_round |
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#ifdef PARANOID |
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/* The logic is wrong if we got here */ |
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L_bugged: |
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pushl EX_INTERNAL|0x202 |
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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_1: |
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pushl EX_INTERNAL|0x203 |
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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|0x204 |
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call EXCEPTION |
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pop %ebx |
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jmp L_exit |
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L_exit: |
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movl $-1,%eax |
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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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#endif /* PARANOID */ |
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SYM_FUNC_END(FPU_u_div)
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