?? i_tofd32.asm
字號:
;******************************************************************************
;* I_TOFD32.ASM - 32 BIT STATE - v2.24 *
;* Copyright (c) 1996-2002 Texas Instruments Incorporated *
;******************************************************************************
;****************************************************************************
;* I_TOFD - CONVERT AN SIGNED 32 BIT INTEGER INTO AN IEEE 754 FORMAT
;* DOUBLE PRECISION FLOATING POINT
;****************************************************************************
;*
;* o INPUT OP IS IN r0
;* o RESULT IS RETURNED IN r0:r1
;*
;****************************************************************************
;*
;* +------------------------------------------------------------------+
;* | DOUBLE PRECISION FLOATING POINT FORMAT |
;* | 64-bit representation |
;* | 31 30 20 19 0 |
;* | +-+----------+---------------------+ |
;* | |S| E | M1 | |
;* | +-+----------+---------------------+ |
;* | |
;* | 31 0 |
;* | +----------------------------------+ |
;* | | M2 | |
;* | +----------------------------------+ |
;* | |
;* | <S> SIGN FIELD : 0 - POSITIVE VALUE |
;* | 1 - NEGATIVE VALUE |
;* | |
;* | <E> EXPONENT FIELD: 0000000000 - ZERO IFF M == 0 |
;* | 0000000001..1111111110 - EXPONENT VALUE(1023 BIAS) |
;* | 1111111111 - INFINITY |
;* | |
;* | <M1:M2> MANTISSA FIELDS: FRACTIONAL MAGNITUDE WITH IMPLIED 1 |
;* +------------------------------------------------------------------+
;*
;****************************************************************************
.state32
.global I_TOFD
I_TOFD: CMP r0, #0 ; IF ZERO, RETURN ZERO
MOVEQ r1, #0 ;
MOVEQ pc, lr ;
RSBMI r1, r0, #0 ; MOVE INPUT AND IF NEGATIVE,
MOVPL r1, r0 ; NEGATE IT
MOV r0, #0x1F ; SETUP THE EXPONENT
ORRMI r0, r0, #0x00000C00 ; AND ENCODE SIGN INTO IT
ORRPL r0, r0, #0x00000400 ;
loop: MOVS r1, r1, LSL #1 ; NORMALIZE THE MANTISSA
SUB r0, r0, #0x1 ; ADJUSTING THE EXPONENT, ACCORDINGLY
BCC loop ;
MOV r0, r0, LSL #20 ; SETUP HIGH HALF OF RESULT
ORR r0, r0, r1, LSR #12 ;
MOV r1, r1, LSL #20 ; SETUP LOW HALF OF RESULT
MOV pc, lr ;
.end
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