ppc_dtoi.s

powerpc 405 优化过的硬浮点库

/* fpopt/ppc_dtoi.S, pl_FPE_common, pl_linux 11/24/03 16:17:24                                                                  */
/*----------------------------------------------------------------------------- */
/*  Copyright (c) 2003, IBM Corporation                                         */
/*  All rights reserved.                                                        */
/*                                                                              */
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/*  without modification, are permitted provided that the following             */
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/*                                                                              */
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/*                                                                              */
/*----------------------------------------------------------------------------- */
/*                                                                              */
/* Function: convert double floating point to 4-byte integer                    */
/* Input:    r3,r4                                                              */
/* Output:   r3                                                                 */
/* Notes:   1. No stack frame is created for this function, so the following    */
/*             registers must be preserved, as required by ABI specification:   */
/*               LR, CR0, R1, R2, R13-R31                                       */
/*          2. operation performed according to IEEE754-1985 standard.          */
/*          3. ISO/ANSI C requires that conversions to integers be rounded      */
/*             toward zero (in short, leftover fraction bits are truncated).    */
/*                                                                              */
/*----------------------------------------------------------------------------- */

#include <ppc4xx.inc>
#include "fpeLib.inc"

function_prolog(__fixdfsi)

/* Save CR in r6                                                                */
     mfcr    r6
/* Load up registers with source double                                         */
/*  r8 = exp  r9 = hifrac r10 = lofrac                                          */
     rlwinm  r9,r3,0,0x000FFFFF      /* extract hifrac */
     rlwinm  r8,r3,12,0x000007FF     /* extract exponent */
/* exponent test for Infinity or xNAN                                           */
     cmpi    cr0,0,r8,2047           /* test for Infinity or NAN */
     beq     Infinity_or_NAN
/* exponent test for large operand                                              */
     cmpi    cr0,0,r8,1053           /* test for large operand */
     bgt     Large_operand
/* Normal operand processing here                                               */
/*  r9 is fraction, left justified                                              */
     rlwinm  r9,r9,10,0x3FFFFc00     /* r9[1:20] = r9[12:31] */
     rlwimi  r9,r4,10,0x000003FF     /* r9[21:31] = r4[0:10] */
     cmpi    cr0,0,r8,0              /* test exp for 0 */
     addic.  r8,r8,-1022             /* exp = exp - 1022 */
     beq     Zero_exp
     addic.  r8,r8,-1                /* exp = exp - 1023 */
     oris    r9,r9,0x4000            /* set hi order bit of r9 */
Zero_exp:
     blt     Zeros                   /* fraction only, return 0 */
     subfic  r0,r8,31
     or.     r0,r0,r0
     mtctr   r0
     b       ltest
cloop:
/* shift frac right by 1, zero fill                                             */
     rlwinm  r9,r9,31,0x7FFFFFFF     /* shift hifrac right by 1, zero fill */
ltest:
     bdnz    cloop

/* Form final result                                                            */
     or.     r3,r3,r3                /* set CR for sign bit */
     bge     fin_pos
/* sign is negative                                                             */
     nand    r9,r9,r9                /* ones comp of r9 */
     addi    r9,r9,1                 /* now 2's complement                   */
fin_pos:
/* check size of result                                                         */
     or.     r3,r9,r9                /* check for zero and set return value  */
     beq     Zeros
     
return_results:                      /* r3 contains signed integer result    */
     mtcr    r6                      /* restore CR */
     blr
     
/* Infinity or a NAN                                                            */
Infinity_or_NAN:
     or.     r0,r9,r4                /* test rest for zero (infinity test)   */
     bne     NAN
/* Infinity if here (also, Large operand)                                       */
Large_operand:
     or.     r3,r3,r3
     blt     Neg_infinity
/* form value for converted positive infinity                                   */
     lis     r3,0x7FFF
     ori     r3,r3,0xFFFF
     b     return_results
Neg_infinity:
     lis     r3,0x8000
     b       return_results
NAN:
     lis     r3,0x8000
     b       return_results
Zeros:
     li      r3,0                    /* Store zero */
     b       return_results
     
function_epilog(__fixdfsi)