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        .file   "reg_u_sub.S"
/*---------------------------------------------------------------------------+
 |  reg_u_sub.S                                                              |
 |                                                                           |
 | Core floating point subtraction routine.                                  |
 |                                                                           |
 | Copyright (C) 1992,1993,1995                                              |
 |                       W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
 |                       Australia.  E-mail billm@jacobi.maths.monash.edu.au |
 |                                                                           |
 | Call from C as:                                                           |
 |   void reg_u_sub(FPU_REG *arg1, FPU_REG *arg2, FPU_REG *answ,             |
 |                                                int control_w)             |
 |                                                                           |
 +---------------------------------------------------------------------------*/

/*
 |    Kernel subtraction routine reg_u_sub(reg *arg1, reg *arg2, reg *answ).
 |    Takes two valid reg f.p. numbers (TW_Valid), which are
 |    treated as unsigned numbers,
 |    and returns their difference as a TW_Valid or TW_Zero f.p.
 |    number.
 |    The first number (arg1) must be the larger.
 |    The returned number is normalized.
 |    Basic checks are performed if PARANOID is defined.
 */

#include "exception.h"
#include "fpu_emu.h"
#include "control_w.h"

.text
ENTRY(reg_u_sub)
        pushl   %ebp
        movl    %esp,%ebp
        pushl   %esi
        pushl   %edi
        pushl   %ebx

        movl    PARAM1,%esi     /* source 1 */
        movl    PARAM2,%edi     /* source 2 */

#ifdef DENORM_OPERAND
        cmpl    EXP_UNDER,EXP(%esi)
        jg      xOp1_not_denorm

        call    SYMBOL_NAME(denormal_operand)
        orl     %eax,%eax
        jnz     fpu_Arith_exit

xOp1_not_denorm:
        cmpl    EXP_UNDER,EXP(%edi)
        jg      xOp2_not_denorm

        call    SYMBOL_NAME(denormal_operand)
        orl     %eax,%eax
        jnz     fpu_Arith_exit

xOp2_not_denorm:
#endif DENORM_OPERAND

        movl    EXP(%esi),%ecx
        subl    EXP(%edi),%ecx  /* exp1 - exp2 */

#ifdef PARANOID
        /* source 2 is always smaller than source 1 */
        js      L_bugged_1

        testl   $0x80000000,SIGH(%edi)  /* The args are assumed to be normalized */
        je      L_bugged_2

        testl   $0x80000000,SIGH(%esi)
        je      L_bugged_2
#endif PARANOID

/*--------------------------------------+
 |      Form a register holding the     |
 |      smaller number                  |
 +--------------------------------------*/
        movl    SIGH(%edi),%eax /* register ms word */
        movl    SIGL(%edi),%ebx /* register ls word */

        movl    PARAM3,%edi     /* destination */
        movl    EXP(%esi),%edx
        movl    %edx,EXP(%edi)  /* Copy exponent to destination */
/*      movb    SIGN(%esi),%dl
        movb    %dl,SIGN(%edi) */       /* Copy the sign from the first arg */

        xorl    %edx,%edx       /* register extension */

/*--------------------------------------+
 |      Shift the temporary register    |
 |      right the required number of    |
 |      places.                         |
 +--------------------------------------*/
L_shift_r:
        cmpl    $32,%ecx                /* shrd only works for 0..31 bits */
        jnc     L_more_than_31

/* less than 32 bits */
        shrd    %cl,%ebx,%edx
        shrd    %cl,%eax,%ebx
        shr     %cl,%eax
        jmp     L_shift_done

L_more_than_31:
        cmpl    $64,%ecx
        jnc     L_more_than_63

        subb    $32,%cl
        jz      L_exactly_32

        shrd    %cl,%eax,%edx
        shr     %cl,%eax
        orl     %ebx,%ebx
        jz      L_more_31_no_low        /* none of the lowest bits is set */

        orl     $1,%edx                 /* record the fact in the extension */

L_more_31_no_low:
        movl    %eax,%ebx
        xorl    %eax,%eax
        jmp     L_shift_done

L_exactly_32:
        movl    %ebx,%edx
        movl    %eax,%ebx
        xorl    %eax,%eax
        jmp     L_shift_done

L_more_than_63:
        cmpw    $65,%cx
        jnc     L_more_than_64

        /* Shift right by 64 bits */
        movl    %eax,%edx
        orl     %ebx,%ebx
        jz      L_more_63_no_low

        orl     $1,%edx
        jmp     L_more_63_no_low

L_more_than_64:
        jne     L_more_than_65

        /* Shift right by 65 bits */
        /* Carry is clear if we get here */
        movl    %eax,%edx
        rcrl    %edx
        jnc     L_shift_65_nc

        orl     $1,%edx
        jmp     L_more_63_no_low

L_shift_65_nc:
        orl     %ebx,%ebx
        jz      L_more_63_no_low

        orl     $1,%edx
        jmp     L_more_63_no_low

L_more_than_65:
        movl    $1,%edx         /* The shifted nr always at least one '1' */

L_more_63_no_low:
        xorl    %ebx,%ebx
        xorl    %eax,%eax

L_shift_done:
L_subtr:
/*------------------------------+
 |      Do the subtraction      |
 +------------------------------*/
        xorl    %ecx,%ecx
        subl    %edx,%ecx
        movl    %ecx,%edx
        movl    SIGL(%esi),%ecx
        sbbl    %ebx,%ecx
        movl    %ecx,%ebx
        movl    SIGH(%esi),%ecx
        sbbl    %eax,%ecx
        movl    %ecx,%eax

#ifdef PARANOID
        /* We can never get a borrow */
        jc      L_bugged
#endif PARANOID

/*--------------------------------------+
 |      Normalize the result            |
 +--------------------------------------*/
        testl   $0x80000000,%eax
        jnz     L_round         /* no shifting needed */

        orl     %eax,%eax
        jnz     L_shift_1       /* shift left 1 - 31 bits */

        orl     %ebx,%ebx
        jnz     L_shift_32      /* shift left 32 - 63 bits */

/*
 *       A rare case, the only one which is non-zero if we got here
 *         is:           1000000 .... 0000
 *                      -0111111 .... 1111 1
 *                       -------------------- 
 *                       0000000 .... 0000 1 
 */

        cmpl    $0x80000000,%edx
        jnz     L_must_be_zero

        /* Shift left 64 bits */
        subl    $64,EXP(%edi)
        xchg    %edx,%eax
        jmp     fpu_reg_round

L_must_be_zero:
#ifdef PARANOID
        orl     %edx,%edx
        jnz     L_bugged_3
#endif PARANOID

        /* The result is zero */
        movb    TW_Zero,TAG(%edi)
        movl    $0,EXP(%edi)            /* exponent */
        movl    $0,SIGL(%edi)
        movl    $0,SIGH(%edi)
        jmp     L_exit          /* %eax contains zero */

L_shift_32:
        movl    %ebx,%eax
        movl    %edx,%ebx
        movl    $0,%edx
        subl    $32,EXP(%edi)   /* Can get underflow here */

/* We need to shift left by 1 - 31 bits */
L_shift_1:
        bsrl    %eax,%ecx       /* get the required shift in %ecx */
        subl    $31,%ecx
        negl    %ecx
        shld    %cl,%ebx,%eax
        shld    %cl,%edx,%ebx
        shl     %cl,%edx
        subl    %ecx,EXP(%edi)  /* Can get underflow here */

L_round:
        jmp     fpu_reg_round   /* Round the result */


#ifdef PARANOID
L_bugged_1:
        pushl   EX_INTERNAL|0x206
        call    EXCEPTION
        pop     %ebx
        jmp     L_error_exit

L_bugged_2:
        pushl   EX_INTERNAL|0x209
        call    EXCEPTION
        pop     %ebx
        jmp     L_error_exit

L_bugged_3:
        pushl   EX_INTERNAL|0x210
        call    EXCEPTION
        pop     %ebx
        jmp     L_error_exit

L_bugged_4:
        pushl   EX_INTERNAL|0x211
        call    EXCEPTION
        pop     %ebx
        jmp     L_error_exit

L_bugged:
        pushl   EX_INTERNAL|0x212
        call    EXCEPTION
        pop     %ebx
        jmp     L_error_exit
#endif PARANOID


L_error_exit:
        movl    $1,%eax
L_exit:
        popl    %ebx
        popl    %edi
        popl    %esi
        leave
        ret