The CICA Windows Explosion!/The CICA Windows Explosion! - Disc 2.iso/programr/dpmigcc5.zip/RSX/SOURCE/FPU-EMU/REG_ROUN.S

Text File | 1994-05-27 | 18KB | 702 lines

    .file "reg_round.S"
/*---------------------------------------------------------------------------+
 |  reg_round.S                                                              |
 |                                                                           |
 | Rounding/truncation/etc for FPU basic arithmetic functions.               |
 |                                                                           |
 | Copyright (C) 1993                                                        |
 |                       W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
 |                       Australia.  E-mail   [e-mail]    |
 |                                                                           |
 | This code has four possible entry points.                                 |
 | The following must be entered by a jmp intruction:                        |
 |   fpu_reg_round, fpu_reg_round_sqrt, and fpu_Arith_exit.                  |
 |                                                                           |
 | The _round_reg entry point is intended to be used by C code.              |
 | From C, call as:                                                          |
 | void round_reg(FPU_REG *arg, unsigned int extent, unsigned int control_w) |
 |                                                                           |
 | 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_asm.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


#ifdef 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 2,0
FPU_bits_lost:
    .byte    0
FPU_denormal:
    .byte    0
#endif REENTRANT_FPU


.text
    .align 2,144
.globl fpu_reg_round
.globl fpu_reg_round_sqrt
.globl fpu_Arith_exit
.globl _round_reg

/* Entry point when called from C */
_round_reg:
    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
    movl    PARAM3,%ecx
    jmp    fpu_reg_round_sqrt

fpu_reg_round:            /* Normal entry point */
    movl    PARAM4,%ecx

fpu_reg_round_sqrt:        /* Entry point from wm_sqrt.S */

#ifdef REENTRANT_FPU
    pushl    %ebx        /* adjust the stack pointer */
#endif REENTRANT_FPU

#ifdef PARANOID
/* Cannot use this here yet */
/*    orl    %eax,%eax */
/*    jns    L_entry_bugged */
#endif PARANOID

    cmpl    EXP_UNDER,EXP(%edi)
    jle    xMake_denorm            /* The number is a de-normal */

    movb    $0,FPU_denormal            /* 0 -> not a de-normal */

xDenorm_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,SIGN(%edi)
    jne    LCheck_truncate_24    /* If negative then  up==truncate */

    jmp    LCheck_24_round_up

LDown_24:
    cmpb    SIGN_POS,SIGN(%edi)
    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_round_up
    jmp    LRe_normalise

LRound_nearest_24:
    /* Do rounding of the 24th bit if needed (nearest or even) */
    movl    %eax,%ecx
    andl    $0x000000ff,%ecx
    cmpl    $0x00000080,%ecx
    jc    LCheck_truncate_24    /* less than half, no increment needed */

    jne    LGreater_Half_24    /* greater than half, increment needed */

    /* Possibly half, we need to check the ls bits */
    orl    %ebx,%ebx
    jnz    LGreater_Half_24    /* greater than half, increment needed */

    orl    %edx,%edx
    jnz    LGreater_Half_24    /* greater than half, increment needed */

    /* Exactly half, increment only if 24th bit is 1 (round to even) */
    testl    $0x00000100,%eax
    jz    LDo_truncate_24

LGreater_Half_24:            /* Rounding: increment at the 24th bit */
LDo_24_round_up:
    andl    $0xffffff00,%eax    /* Truncate to 24 bits */
    xorl    %ebx,%ebx
    movb    LOST_UP,FPU_bits_lost
    addl    $0x00000100,%eax
    jmp    LCheck_Round_Overflow

LCheck_truncate_24:
    movl    %eax,%ecx
    andl    $0x000000ff,%ecx
    orl    %ebx,%ecx
    orl    %edx,%ecx
    jz    LRe_normalise        /* No truncation needed */

LDo_truncate_24:
    andl    $0xffffff00,%eax    /* Truncate to 24 bits */
    xorl    %ebx,%ebx
    movb    LOST_DOWN,FPU_bits_lost
    jmp    LRe_normalise


/* Round etc to 53 bit precision */
LRound_To_53:
    movl    %esi,%ecx
    andl    CW_RC,%ecx
    cmpl    RC_RND,%ecx
    je    LRound_nearest_53

    cmpl    RC_CHOP,%ecx
    je    LCheck_truncate_53

    cmpl    RC_UP,%ecx        /* Towards +infinity */
    je    LUp_53

    cmpl    RC_DOWN,%ecx        /* Towards -infinity */
    je    LDown_53

#ifdef PARANOID
    jmp    L_bugged_round53
#endif PARANOID

LUp_53:
    cmpb    SIGN_POS,SIGN(%edi)
    jne    LCheck_truncate_53    /* If negative then  up==truncate */

    jmp    LCheck_53_round_up

LDown_53:
    cmpb    SIGN_POS,SIGN(%edi)
    je    LCheck_truncate_53    /* If positive then  down==truncate */

LCheck_53_round_up:
    movl    %ebx,%ecx
    andl    $0x000007ff,%ecx
    orl    %edx,%ecx
    jnz    LDo_53_round_up
    jmp    LRe_normalise

LRound_nearest_53:
    /* Do rounding of the 53rd bit if needed (nearest or even) */
    movl    %ebx,%ecx
    andl    $0x000007ff,%ecx
    cmpl    $0x00000400,%ecx
    jc    LCheck_truncate_53    /* less than half, no increment needed */

    jnz    LGreater_Half_53    /* greater than half, increment needed */

    /* Possibly half, we need to check the ls bits */
    orl    %edx,%edx
    jnz    LGreater_Half_53    /* greater than half, increment needed */

    /* Exactly half, increment only if 53rd bit is 1 (round to even) */
    testl    $0x00000800,%ebx
    jz    LTruncate_53

LGreater_Half_53:            /* Rounding: increment at the 53rd bit */
LDo_53_round_up:
    movb    LOST_UP,FPU_bits_lost
    andl    $0xfffff800,%ebx    /* Truncate to 53 bits */
    addl    $0x00000800,%ebx
    adcl    $0,%eax
    jmp    LCheck_Round_Overflow

LCheck_truncate_53:
    movl    %ebx,%ecx
    andl    $0x000007ff,%ecx
    orl    %edx,%ecx
    jz    LRe_normalise

LTruncate_53:
    movb    LOST_DOWN,FPU_bits_lost
    andl    $0xfffff800,%ebx    /* Truncate to 53 bits */
    jmp    LRe_normalise


/* Round etc to 64 bit precision */
LRound_To_64:
    movl    %esi,%ecx
    andl    CW_RC,%ecx
    cmpl    RC_RND,%ecx
    je    LRound_nearest_64

    cmpl    RC_CHOP,%ecx
    je    LCheck_truncate_64

    cmpl    RC_UP,%ecx        /* Towards +infinity */
    je    LUp_64

    cmpl    RC_DOWN,%ecx        /* Towards -infinity */
    je    LDown_64

#ifdef PARANOID
    jmp    L_bugged_round64
#endif PARANOID

LUp_64:
    cmpb    SIGN_POS,SIGN(%edi)
    jne    LCheck_truncate_64    /* If negative then  up==truncate */

    orl    %edx,%edx
    jnz    LDo_64_round_up
    jmp    LRe_normalise

LDown_64:
    cmpb    SIGN_POS,SIGN(%edi)
    je    LCheck_truncate_64    /* If positive then  down==truncate */

    orl    %edx,%edx
    jnz    LDo_64_round_up
    jmp    LRe_normalise

LRound_nearest_64:
    cmpl    $0x80000000,%edx
    jc    LCheck_truncate_64

    jne    LDo_64_round_up

    /* Now test for round-to-even */
    testb    $1,%ebx
    jz    LCheck_truncate_64

LDo_64_round_up:
    movb    LOST_UP,FPU_bits_lost
    addl    $1,%ebx
    adcl    $0,%eax

LCheck_Round_Overflow:
    jnc    LRe_normalise

    /* Overflow, adjust the result (significand to 1.0) */
    rcrl    $1,%eax
    rcrl    $1,%ebx
    incl    EXP(%edi)
    jmp    LRe_normalise

LCheck_truncate_64:
    orl    %edx,%edx
    jz    LRe_normalise

LTruncate_64:
    movb    LOST_DOWN,FPU_bits_lost

LRe_normalise:
    testb    $0xff,FPU_denormal
    jnz    xNormalise_result

xL_Normalised:
    cmpb    LOST_UP,FPU_bits_lost
    je    xL_precision_lost_up

    cmpb    LOST_DOWN,FPU_bits_lost
    je    xL_precision_lost_down

xL_no_precision_loss:
    /* store the result */
    movb    TW_Valid,TAG(%edi)

xL_Store_significand:
    movl    %eax,SIGH(%edi)
    movl    %ebx,SIGL(%edi)

    xorl    %eax,%eax    /* No errors detected. */

    cmpl    EXP_OVER,EXP(%edi)
    jge    L_overflow

fpu_reg_round_exit:
#ifdef REENTRANT_FPU
    popl    %ebx        /* adjust the stack pointer */
#endif REENTRANT_FPU

fpu_Arith_exit:
    popl    %ebx
    popl    %edi
    popl    %esi
    leave
    ret


/*
 * Set the FPU status flags to represent precision loss due to
 * round-up.
 */
xL_precision_lost_up:
    push    %eax
    call    _set_precision_flag_up
    popl    %eax
    jmp    xL_no_precision_loss

/*
 * Set the FPU status flags to represent precision loss due to
 * truncation.
 */
xL_precision_lost_down:
    push    %eax
    call    _set_precision_flag_down
    popl    %eax
    jmp    xL_no_precision_loss


/*
 * The number is a denormal (which might get rounded up to a normal)
 * Shift the number right the required number of bits, which will
 * have to be undone later...
 */
xMake_denorm:
    /* The action to be taken depends upon whether the underflow
       exception is masked */
    testb    CW_Underflow,%cl        /* Underflow mask. */
    jz    xUnmasked_underflow        /* Do not make a denormal. */

    movb    DENORMAL,FPU_denormal

    pushl    %ecx        /* Save */
    movl    EXP_UNDER+1,%ecx
    subl    EXP(%edi),%ecx

    cmpl    $64,%ecx    /* shrd only works for 0..31 bits */
    jnc    xDenorm_shift_more_than_63

    cmpl    $32,%ecx    /* shrd only works for 0..31 bits */
    jnc    xDenorm_shift_more_than_32

/*
 * We got here without jumps by assuming that the most common requirement
 *   is for a small de-normalising shift.
 * Shift by [1..31] bits
 */
    addl    %ecx,EXP(%edi)
    orl    %edx,%edx    /* extension */
    setne    %ch        /* Save whether %edx is non-zero */
    xorl    %edx,%edx
    shrd    %cl,%ebx,%edx
    shrd    %cl,%eax,%ebx
    shr    %cl,%eax
    orb    %ch,%dl
    popl    %ecx
    jmp    xDenorm_done

/* Shift by [32..63] bits */
xDenorm_shift_more_than_32:
    addl    %ecx,EXP(%edi)
    subb    $32,%cl
    orl    %edx,%edx
    setne    %ch
    orb    %ch,%bl
    xorl    %edx,%edx
    shrd    %cl,%ebx,%edx
    shrd    %cl,%eax,%ebx
    shr    %cl,%eax
    orl    %edx,%edx        /* test these 32 bits */
    setne    %cl
    orb    %ch,%bl
    orb    %cl,%bl
    movl    %ebx,%edx
    movl    %eax,%ebx
    xorl    %eax,%eax
    popl    %ecx
    jmp    xDenorm_done

/* Shift by [64..) bits */
xDenorm_shift_more_than_63:
    cmpl    $64,%ecx
    jne    xDenorm_shift_more_than_64

/* Exactly 64 bit shift */
    addl    %ecx,EXP(%edi)
    xorl    %ecx,%ecx
    orl    %edx,%edx
    setne    %cl
    orl    %ebx,%ebx
    setne    %ch
    orb    %ch,%cl
    orb    %cl,%al
    movl    %eax,%edx
    xorl    %eax,%eax
    xorl    %ebx,%ebx
    popl    %ecx
    jmp    xDenorm_done

xDenorm_shift_more_than_64:
    movl    EXP_UNDER+1,EXP(%edi)
/* This is easy, %eax must be non-zero, so.. */
    movl    $1,%edx
    xorl    %eax,%eax
    xorl    %ebx,%ebx
    popl    %ecx
    jmp    xDenorm_done


xUnmasked_underflow:
    movb    UNMASKED_UNDERFLOW,FPU_denormal
    jmp    xDenorm_done


/* Undo the de-normalisation. */
xNormalise_result:
    cmpb    UNMASKED_UNDERFLOW,FPU_denormal
    je    xSignal_underflow

/* The number must be a denormal if we got here. */
#ifdef PARANOID
    /* But check it... just in case. */
    cmpl    EXP_UNDER+1,EXP(%edi)
    jne    L_norm_bugged
#endif PARANOID

#ifdef PECULIAR_486
    /*
     * This implements a special feature of 80486 behaviour.
     * Underflow will be signalled even if the number is
     * not a denormal after rounding.
     * This difference occurs only for masked underflow, and not
     * in the unmasked case.
     * Actual 80486 behaviour differs from this in some circumstances.
     */
    orl    %eax,%eax        /* ms bits */
    js    LNormalise_shift_done    /* Will be masked underflow */
#endif PECULIAR_486

    orl    %eax,%eax        /* ms bits */
    js    xL_Normalised        /* No longer a denormal */

    jnz    LNormalise_shift_up_to_31    /* Shift left 0 - 31 bits */

    orl    %ebx,%ebx
    jz    L_underflow_to_zero    /* The contents are zero */

/* Shift left 32 - 63 bits */
    movl    %ebx,%eax
    xorl    %ebx,%ebx
    subl    $32,EXP(%edi)

LNormalise_shift_up_to_31:
    bsrl    %eax,%ecx    /* get the required shift in %ecx */
    subl    $31,%ecx
    negl    %ecx
    shld    %cl,%ebx,%eax
    shl    %cl,%ebx
    subl    %ecx,EXP(%edi)

LNormalise_shift_done:
    testb    $0xff,FPU_bits_lost    /* bits lost == underflow */
    jz    xL_Normalised

    /* There must be a masked underflow */
    push    %eax
    pushl    EX_Underflow
    call    _exception
    popl    %eax
    popl    %eax
    jmp    xL_Normalised


/*
 * The operations resulted in a number too small to represent.
 * Masked response.
 */
L_underflow_to_zero:
    push    %eax
    call    _set_precision_flag_down
    popl    %eax

    push    %eax
    pushl    EX_Underflow
    call    _exception
    popl    %eax
    popl    %eax

/* Reduce the exponent to EXP_UNDER */
    movl    EXP_UNDER,EXP(%edi)
    movb    TW_Zero,TAG(%edi)
    jmp    xL_Store_significand


/* The operations resulted in a number too large to represent. */
L_overflow:
    push    %edi
    call    _arith_overflow
    pop    %edi
    jmp    fpu_reg_round_exit


xSignal_underflow:
    /* The number may have been changed to a non-denormal */
    /* by the rounding operations. */
    cmpl    EXP_UNDER,EXP(%edi)
    jle    xDo_unmasked_underflow

    jmp    xL_Normalised

xDo_unmasked_underflow:
    /* Increase the exponent by the magic number */
    addl    $(3*(1<<13)),EXP(%edi)
    push    %eax
    pushl    EX_Underflow
    call    EXCEPTION
    popl    %eax
    popl    %eax
    jmp    xL_Normalised


#ifdef PARANOID
#ifdef PECULIAR_486
L_bugged_denorm_486:
    pushl    EX_INTERNAL|0x236
    call    EXCEPTION
    popl    %ebx
    jmp    L_exception_exit
#else
L_bugged_denorm:
    pushl    EX_INTERNAL|0x230
    call    EXCEPTION
    popl    %ebx
    jmp    L_exception_exit
#endif PECULIAR_486

L_bugged_round24:
    pushl    EX_INTERNAL|0x231
    call    EXCEPTION
    popl    %ebx
    jmp    L_exception_exit

L_bugged_round53:
    pushl    EX_INTERNAL|0x232
    call    EXCEPTION
    popl    %ebx
    jmp    L_exception_exit

L_bugged_round64:
    pushl    EX_INTERNAL|0x233
    call    EXCEPTION
    popl    %ebx
    jmp    L_exception_exit

L_norm_bugged:
    pushl    EX_INTERNAL|0x234
    call    EXCEPTION
    popl    %ebx
    jmp    L_exception_exit

L_entry_bugged:
    pushl    EX_INTERNAL|0x235
    call    EXCEPTION
    popl    %ebx
L_exception_exit:
    mov    $1,%eax
    jmp    fpu_reg_round_exit
#endif PARANOID