.file "reg_u_div.S"
/*---------------------------------------------------------------------------+
| reg_u_div.S |
| |
| Divide one FPU_REG by another and put the result in a destination FPU_REG.|
| |
| Copyright (C) 1992,1993,1995,1997 |
| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
| E-mail billm@suburbia.net |
| |
| |
+---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------+
| Call from C as: |
| int FPU_u_div(FPU_REG *a, FPU_REG *b, FPU_REG *dest, |
| unsigned int control_word, char *sign) |
| |
| Does not compute the destination exponent, but does adjust it. |
| |
| Return value is the tag of the answer, or-ed with FPU_Exception if |
| one was raised, or -1 on internal error. |
+---------------------------------------------------------------------------*/
#include "exception.h"
#include "fpu_emu.h"
#include "control_w.h"
/* #define dSIGL(x) (x) */
/* #define dSIGH(x) 4(x) */
#ifndef NON_REENTRANT_FPU
/*
Local storage on the stack:
Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
Overflow flag: ovfl_flag
*/
#define FPU_accum_3 -4(%ebp)
#define FPU_accum_2 -8(%ebp)
#define FPU_accum_1 -12(%ebp)
#define FPU_accum_0 -16(%ebp)
#define FPU_result_1 -20(%ebp)
#define FPU_result_2 -24(%ebp)
#define FPU_ovfl_flag -28(%ebp)
#else
.data
/*
Local storage in a static area:
Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
Overflow flag: ovfl_flag
*/
.align 4,0
FPU_accum_3:
.long 0
FPU_accum_2:
.long 0
FPU_accum_1:
.long 0
FPU_accum_0:
.long 0
FPU_result_1:
.long 0
FPU_result_2:
.long 0
FPU_ovfl_flag:
.byte 0
#endif /* NON_REENTRANT_FPU */
#define REGA PARAM1
#define REGB PARAM2
#define DEST PARAM3
.text
ENTRY(FPU_u_div)
pushl %ebp
movl %esp,%ebp
#ifndef NON_REENTRANT_FPU
subl $28,%esp
#endif /* NON_REENTRANT_FPU */
pushl %esi
pushl %edi
pushl %ebx
movl REGA,%esi
movl REGB,%ebx
movl DEST,%edi
movswl EXP(%esi),%edx
movswl EXP(%ebx),%eax
subl %eax,%edx
addl EXP_BIAS,%edx
/* A denormal and a large number can cause an exponent underflow */
cmpl EXP_WAY_UNDER,%edx
jg xExp_not_underflow
/* Set to a really low value allow correct handling */
movl EXP_WAY_UNDER,%edx
xExp_not_underflow:
movw %dx,EXP(%edi)
#ifdef PARANOID
/* testl $0x80000000, SIGH(%esi) // Dividend */
/* je L_bugged */
testl $0x80000000, SIGH(%ebx) /* Divisor */
je L_bugged
#endif /* PARANOID */
/* Check if the divisor can be treated as having just 32 bits */
cmpl $0,SIGL(%ebx)
jnz L_Full_Division /* Can't do a quick divide */
/* We should be able to zip through the division here */
movl SIGH(%ebx),%ecx /* The divisor */
movl SIGH(%esi),%edx /* Dividend */
movl SIGL(%esi),%eax /* Dividend */
cmpl %ecx,%edx
setaeb FPU_ovfl_flag /* Keep a record */
jb L_no_adjust
subl %ecx,%edx /* Prevent the overflow */
L_no_adjust:
/* Divide the 64 bit number by the 32 bit denominator */
divl %ecx
movl %eax,FPU_result_2
/* Work on the remainder of the first division */
xorl %eax,%eax
divl %ecx
movl %eax,FPU_result_1
/* Work on the remainder of the 64 bit division */
xorl %eax,%eax
divl %ecx
testb $255,FPU_ovfl_flag /* was the num > denom ? */
je L_no_overflow
/* Do the shifting here */
/* increase the exponent */
incw EXP(%edi)
/* shift the mantissa right one bit */
stc /* To set the ms bit */
rcrl FPU_result_2
rcrl FPU_result_1
rcrl %eax
L_no_overflow:
jmp LRound_precision /* Do the rounding as required */
/*---------------------------------------------------------------------------+
| Divide: Return arg1/arg2 to arg3. |
| |
| This routine does not use the exponents of arg1 and arg2, but does |
| adjust the exponent of arg3. |
| |
| The maximum returned value is (ignoring exponents) |
| .ffffffff ffffffff |
| ------------------ = 1.ffffffff fffffffe |
| .80000000 00000000 |
| and the minimum is |
| .80000000 00000000 |
| ------------------ = .80000000 00000001 (rounded) |
| .ffffffff ffffffff |
| |
+---------------------------------------------------------------------------*/
L_Full_Division:
/* Save extended dividend in local register */
movl SIGL(%esi),%eax
movl %eax,FPU_accum_2
movl SIGH(%esi),%eax
movl %eax,FPU_accum_3
xorl %eax,%eax
movl %eax,FPU_accum_1 /* zero the extension */
movl %eax,FPU_accum_0 /* zero the extension */
movl SIGL(%esi),%eax /* Get the current num */
movl SIGH(%esi),%edx
/*----------------------------------------------------------------------*/
/* Initialization done.
Do the first 32 bits. */
movb $0,FPU_ovfl_flag
cmpl SIGH(%ebx),%edx /* Test for imminent overflow */
jb LLess_than_1
ja LGreater_than_1
cmpl SIGL(%ebx),%eax
jb LLess_than_1
LGreater_than_1:
/* The dividend is greater or equal, would cause overflow */
setaeb FPU_ovfl_flag /* Keep a record */
subl SIGL(%ebx),%eax
sbbl SIGH(%ebx),%edx /* Prevent the overflow */
movl %eax,FPU_accum_2
movl %edx,FPU_accum_3
LLess_than_1:
/* At this point, we have a dividend < divisor, with a record of
adjustment in FPU_ovfl_flag */
/* We will divide by a number which is too large */
movl SIGH(%ebx),%ecx
addl $1,%ecx
jnc LFirst_div_not_1
/* here we need to divide by 100000000h,
i.e., no division at all.. */
mov %edx,%eax
jmp LFirst_div_done
LFirst_div_not_1:
divl %ecx /* Divide the numerator by the augmented
denom ms dw */
LFirst_div_done:
movl %eax,FPU_result_2 /* Put the result in the answer */
mull SIGH(%ebx) /* mul by the ms dw of the denom */
subl %eax,FPU_accum_2 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_3
movl FPU_result_2,%eax /* Get the result back */
mull SIGL(%ebx) /* now mul the ls dw of the denom */
subl %eax,FPU_accum_1 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_2
sbbl $0,FPU_accum_3
je LDo_2nd_32_bits /* Must check for non-zero result here */
#ifdef PARANOID
jb L_bugged_1
#endif /* PARANOID */
/* need to subtract another once of the denom */
incl FPU_result_2 /* Correct the answer */
movl SIGL(%ebx),%eax
movl SIGH(%ebx),%edx
subl %eax,FPU_accum_1 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_2
#ifdef PARANOID
sbbl $0,FPU_accum_3
jne L_bugged_1 /* Must check for non-zero result here */
#endif /* PARANOID */
/*----------------------------------------------------------------------*/
/* Half of the main problem is done, there is just a reduced numerator
to handle now.
Work with the second 32 bits, FPU_accum_0 not used from now on */
LDo_2nd_32_bits:
movl FPU_accum_2,%edx /* get the reduced num */
movl FPU_accum_1,%eax
/* need to check for possible subsequent overflow */
cmpl SIGH(%ebx),%edx
jb LDo_2nd_div
ja LPrevent_2nd_overflow
cmpl SIGL(%ebx),%eax
jb LDo_2nd_div
LPrevent_2nd_overflow:
/* The numerator is greater or equal, would cause overflow */
/* prevent overflow */
subl SIGL(%ebx),%eax
sbbl SIGH(%ebx),%edx
movl %edx,FPU_accum_2
movl %eax,FPU_accum_1
incl FPU_result_2 /* Reflect the subtraction in the answer */
#ifdef PARANOID
je L_bugged_2 /* Can't bump the result to 1.0 */
#endif /* PARANOID */
LDo_2nd_div:
cmpl $0,%ecx /* augmented denom msw */
jnz LSecond_div_not_1
/* %ecx == 0, we are dividing by 1.0 */
mov %edx,%eax
jmp LSecond_div_done
LSecond_div_not_1:
divl %ecx /* Divide the numerator by the denom ms dw */
LSecond_div_done:
movl %eax,FPU_result_1 /* Put the result in the answer */
mull SIGH(%ebx) /* mul by the ms dw of the denom */
subl %eax,FPU_accum_1 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_2
#ifdef PARANOID
jc L_bugged_2
#endif /* PARANOID */
movl FPU_result_1,%eax /* Get the result back */
mull SIGL(%ebx) /* now mul the ls dw of the denom */
subl %eax,FPU_accum_0 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_1 /* Subtract from the num local reg */
sbbl $0,FPU_accum_2
#ifdef PARANOID
jc L_bugged_2
#endif /* PARANOID */
jz LDo_3rd_32_bits
#ifdef PARANOID
cmpl $1,FPU_accum_2
jne L_bugged_2
#endif /* PARANOID */
/* need to subtract another once of the denom */
movl SIGL(%ebx),%eax
movl SIGH(%ebx),%edx
subl %eax,FPU_accum_0 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_1
sbbl $0,FPU_accum_2
#ifdef PARANOID
jc L_bugged_2
jne L_bugged_2
#endif /* PARANOID */
addl $1,FPU_result_1 /* Correct the answer */
adcl $0,FPU_result_2
#ifdef PARANOID
jc L_bugged_2 /* Must check for non-zero result here */
#endif /* PARANOID */
/*----------------------------------------------------------------------*/
/* The division is essentially finished here, we just need to perform
tidying operations.
Deal with the 3rd 32 bits */
LDo_3rd_32_bits:
movl FPU_accum_1,%edx /* get the reduced num */
movl FPU_accum_0,%eax
/* need to check for possible subsequent overflow */
cmpl SIGH(%ebx),%edx /* denom */
jb LRound_prep
ja LPrevent_3rd_overflow
cmpl SIGL(%ebx),%eax /* denom */
jb LRound_prep
LPrevent_3rd_overflow:
/* prevent overflow */
subl SIGL(%ebx),%eax
sbbl SIGH(%ebx),%edx
movl %edx,FPU_accum_1
movl %eax,FPU_accum_0
addl $1,FPU_result_1 /* Reflect the subtraction in the answer */
adcl $0,FPU_result_2
jne LRound_prep
jnc LRound_prep
/* This is a tricky spot, there is an overflow of the answer */
movb $255,FPU_ovfl_flag /* Overflow -> 1.000 */
LRound_prep:
/*
* Prepare for rounding.
* To test for rounding, we just need to compare 2*accum with the
* denom.
*/
movl FPU_accum_0,%ecx
movl FPU_accum_1,%edx
movl %ecx,%eax
orl %edx,%eax
jz LRound_ovfl /* The accumulator contains zero. */
/* Multiply by 2 */
clc
rcll $1,%ecx
rcll $1,%edx
jc LRound_large /* No need to compare, denom smaller */
subl SIGL(%ebx),%ecx
sbbl SIGH(%ebx),%edx
jnc LRound_not_small
movl $0x70000000,%eax /* Denom was larger */
jmp LRound_ovfl
LRound_not_small:
jnz LRound_large
movl $0x80000000,%eax /* Remainder was exactly 1/2 denom */
jmp LRound_ovfl
LRound_large:
movl $0xff000000,%eax /* Denom was smaller */
LRound_ovfl:
/* We are now ready to deal with rounding, but first we must get
the bits properly aligned */
testb $255,FPU_ovfl_flag /* was the num > denom ? */
je LRound_precision
incw EXP(%edi)
/* shift the mantissa right one bit */
stc /* Will set the ms bit */
rcrl FPU_result_2
rcrl FPU_result_1
rcrl %eax
/* Round the result as required */
LRound_precision:
decw EXP(%edi) /* binary point between 1st & 2nd bits */
movl %eax,%edx
movl FPU_result_1,%ebx
movl FPU_result_2,%eax
jmp fpu_reg_round
#ifdef PARANOID
/* The logic is wrong if we got here */
L_bugged:
pushl EX_INTERNAL|0x202
call EXCEPTION
pop %ebx
jmp L_exit
L_bugged_1:
pushl EX_INTERNAL|0x203
call EXCEPTION
pop %ebx
jmp L_exit
L_bugged_2:
pushl EX_INTERNAL|0x204
call EXCEPTION
pop %ebx
jmp L_exit
L_exit:
movl $-1,%eax
popl %ebx
popl %edi
popl %esi
leave
ret
#endif /* PARANOID */
