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| /* SPDX-License-Identifier: GPL-2.0 */
| .file "reg_u_sub.S"
| /*---------------------------------------------------------------------------+
| | reg_u_sub.S |
| | |
| | Core floating point subtraction routine. |
| | |
| | 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_sub(FPU_REG *arg1, FPU_REG *arg2, FPU_REG *answ, |
| | 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. |
| | |
| +---------------------------------------------------------------------------*/
|
| /*
| | Kernel subtraction routine FPU_u_sub(reg *arg1, reg *arg2, reg *answ).
| | Takes two valid reg f.p. numbers (TAG_Valid), which are
| | treated as unsigned numbers,
| | and returns their difference as a TAG_Valid or TAG_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
| SYM_FUNC_START(FPU_u_sub)
| pushl %ebp
| movl %esp,%ebp
| pushl %esi
| pushl %edi
| pushl %ebx
|
| movl PARAM1,%esi /* source 1 */
| movl PARAM2,%edi /* source 2 */
|
| movl PARAM6,%ecx
| subl PARAM7,%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 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 PARAM6,%edx
| movw %dx,EXP(%edi) /* Copy exponent to destination */
|
| xorl %edx,%edx /* register extension */
|
| /*--------------------------------------+
| | Shift the temporary register |
| | right the required number of |
| | places. |
| +--------------------------------------*/
|
| cmpw $32,%cx /* 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:
| cmpw $64,%cx
| 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 */
| subw $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 */
| movw $0,EXP(%edi) /* exponent */
| movl $0,SIGL(%edi)
| movl $0,SIGH(%edi)
| movl TAG_Zero,%eax
| jmp L_exit
|
| L_shift_32:
| movl %ebx,%eax
| movl %edx,%ebx
| movl $0,%edx
| subw $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
| subw %cx,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
|
| L_error_exit:
| movl $-1,%eax
|
| #endif /* PARANOID */
|
| L_exit:
| popl %ebx
| popl %edi
| popl %esi
| leave
| RET
| SYM_FUNC_END(FPU_u_sub)
|
|
