.file "reg_round.S"
/*---------------------------------------------------------------------------+
| reg_round.S |
| |
| Rounding/truncation/etc for FPU basic arithmetic functions. |
| |
| Copyright (C) 1993,1995,1997 |
| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, |
| Australia. E-mail [email protected] |
| |
| This code has four possible entry points. |
| The following must be entered by a jmp instruction: |
| fpu_reg_round, fpu_reg_round_sqrt, and fpu_Arith_exit. |
| |
| The FPU_round entry point is intended to be used by C code. |
| From C, call as: |
| int FPU_round(FPU_REG *arg, unsigned int extent, unsigned int control_w) |
| |
| Return value is the tag of the answer, or-ed with FPU_Exception if |
| one was raised, or -1 on internal error. |
| |
| For correct "up" and "down" rounding, the argument must have the correct |
| sign. |
| |
+---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------+
| Four entry points. |
| |
| Needed by both the fpu_reg_round and fpu_reg_round_sqrt entry points: |
| %eax:%ebx 64 bit significand |
| %edx 32 bit extension of the significand |
| %edi pointer to an FPU_REG for the result to be stored |
| stack calling function must have set up a C stack frame and |
| pushed %esi, %edi, and %ebx |
| |
| Needed just for the fpu_reg_round_sqrt entry point: |
| %cx A control word in the same format as the FPU control word. |
| Otherwise, PARAM4 must give such a value. |
| |
| |
| The significand and its extension are assumed to be exact in the |
| following sense: |
| If the significand by itself is the exact result then the significand |
| extension (%edx) must contain 0, otherwise the significand extension |
| must be non-zero. |
| If the significand extension is non-zero then the significand is |
| smaller than the magnitude of the correct exact result by an amount |
| greater than zero and less than one ls bit of the significand. |
| The significand extension is only required to have three possible |
| non-zero values: |
| less than 0x80000000 <=> the significand is less than 1/2 an ls |
| bit smaller than the magnitude of the |
| true exact result. |
| exactly 0x80000000 <=> the significand is exactly 1/2 an ls bit |
| smaller than the magnitude of the true |
| exact result. |
| greater than 0x80000000 <=> the significand is more than 1/2 an ls |
| bit smaller than the magnitude of the |
| true exact result. |
| |
+---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------+
| The code in this module has become quite complex, but it should handle |
| all of the FPU flags which are set at this stage of the basic arithmetic |
| computations. |
| There are a few rare cases where the results are not set identically to |
| a real FPU. These require a bit more thought because at this stage the |
| results of the code here appear to be more consistent... |
| This may be changed in a future version. |
+---------------------------------------------------------------------------*/
#include "fpu_emu.h"
#include "exception.h"
#include "control_w.h"
/* Flags for FPU_bits_lost */
#define LOST_DOWN $1
#define LOST_UP $2
/* Flags for FPU_denormal */
#define DENORMAL $1
#define UNMASKED_UNDERFLOW $2
#ifndef NON_REENTRANT_FPU
/* Make the code re-entrant by putting
local storage on the stack: */
#define FPU_bits_lost (%esp)
#define FPU_denormal 1(%esp)
#else
/* Not re-entrant, so we can gain speed by putting
local storage in a static area: */
.data
.align 4,0
FPU_bits_lost:
.byte 0
FPU_denormal:
.byte 0
#endif /* NON_REENTRANT_FPU */
.text
.globl fpu_reg_round
.globl fpu_Arith_exit
/* Entry point when called from C */
ENTRY(FPU_round)
pushl %ebp
movl %esp,%ebp
pushl %esi
pushl %edi
pushl %ebx
movl PARAM1,%edi
movl SIGH(%edi),%eax
movl SIGL(%edi),%ebx
movl PARAM2,%edx
fpu_reg_round: /* Normal entry point */
movl PARAM4,%ecx
#ifndef NON_REENTRANT_FPU
pushl %ebx /* adjust the stack pointer */
#endif /* NON_REENTRANT_FPU */
#ifdef PARANOID
/* Cannot use this here yet */
/* orl %eax,%eax */
/* jns L_entry_bugged */
#endif /* PARANOID */
cmpw EXP_UNDER,EXP(%edi)
jle L_Make_denorm /* The number is a de-normal */
movb $0,FPU_denormal /* 0 -> not a de-normal */
Denorm_done:
movb $0,FPU_bits_lost /* No bits yet lost in rounding */
movl %ecx,%esi
andl CW_PC,%ecx
cmpl PR_64_BITS,%ecx
je LRound_To_64
cmpl PR_53_BITS,%ecx
je LRound_To_53
cmpl PR_24_BITS,%ecx
je LRound_To_24
#ifdef PECULIAR_486
/* With the precision control bits set to 01 "(reserved)", a real 80486
behaves as if the precision control bits were set to 11 "64 bits" */
cmpl PR_RESERVED_BITS,%ecx
je LRound_To_64
#ifdef PARANOID
jmp L_bugged_denorm_486
#endif /* PARANOID */
#else
#ifdef PARANOID
jmp L_bugged_denorm /* There is no bug, just a bad control word */
#endif /* PARANOID */
#endif /* PECULIAR_486 */
/* Round etc to 24 bit precision */
LRound_To_24:
movl %esi,%ecx
andl CW_RC,%ecx
cmpl RC_RND,%ecx
je LRound_nearest_24
cmpl RC_CHOP,%ecx
je LCheck_truncate_24
cmpl RC_UP,%ecx /* Towards +infinity */
je LUp_24
cmpl RC_DOWN,%ecx /* Towards -infinity */
je LDown_24
#ifdef PARANOID
jmp L_bugged_round24
#endif /* PARANOID */
LUp_24:
cmpb SIGN_POS,PARAM5
jne LCheck_truncate_24 /* If negative then up==truncate */
jmp LCheck_24_round_up
LDown_24:
cmpb SIGN_POS,PARAM5
je LCheck_truncate_24 /* If positive then down==truncate */
LCheck_24_round_up:
movl %eax,%ecx
andl $0x000000ff,%ecx
orl %ebx,%ecx
orl %edx,%ecx
jnz LDo_24
