mirror of
https://github.com/netwide-assembler/nasm.git
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404 lines
9.3 KiB
C
404 lines
9.3 KiB
C
/* float.c floating-point constant support for the Netwide Assembler
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*
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* The Netwide Assembler is copyright (C) 1996 Simon Tatham and
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* Julian Hall. All rights reserved. The software is
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* redistributable under the licence given in the file "Licence"
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* distributed in the NASM archive.
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*
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* initial version 13/ix/96 by Simon Tatham
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include "nasm.h"
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#define TRUE 1
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#define FALSE 0
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#define MANT_WORDS 6 /* 64 bits + 32 for accuracy == 96 */
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#define MANT_DIGITS 28 /* 29 digits don't fit in 96 bits */
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/*
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* guaranteed top bit of from is set
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* => we only have to worry about _one_ bit shift to the left
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*/
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static int ieee_multiply(unsigned short *to, unsigned short *from)
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{
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unsigned long temp[MANT_WORDS*2];
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int i, j;
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for (i=0; i<MANT_WORDS*2; i++)
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temp[i] = 0;
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for (i=0; i<MANT_WORDS; i++)
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for (j=0; j<MANT_WORDS; j++) {
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unsigned long n;
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n = (unsigned long)to[i] * (unsigned long)from[j];
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temp[i+j] += n >> 16;
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temp[i+j+1] += n & 0xFFFF;
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}
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for (i=MANT_WORDS*2; --i ;) {
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temp[i-1] += temp[i] >> 16;
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temp[i] &= 0xFFFF;
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}
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if (temp[0] & 0x8000) {
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for (i=0; i<MANT_WORDS; i++)
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to[i] = temp[i] & 0xFFFF;
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return 0;
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} else {
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for (i=0; i<MANT_WORDS; i++)
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to[i] = (temp[i] << 1) + !!(temp[i+1] & 0x8000);
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return -1;
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}
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}
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static void ieee_flconvert(char *string, unsigned short *mant, long *exponent,
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efunc error)
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{
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char digits[MANT_DIGITS];
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char *p, *q, *r;
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unsigned short mult[MANT_WORDS], bit;
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unsigned short * m;
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long tenpwr, twopwr;
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int extratwos, started, seendot;
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p = digits;
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tenpwr = 0;
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started = seendot = FALSE;
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while (*string && *string != 'E' && *string != 'e') {
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if (*string == '.') {
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if (!seendot)
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seendot = TRUE;
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else {
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error (ERR_NONFATAL,
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"too many periods in floating-point constant");
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return;
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}
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} else if (*string >= '0' && *string <= '9') {
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if (*string == '0' && !started) {
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if (seendot)
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tenpwr--;
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} else {
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started = TRUE;
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if (p < digits+sizeof(digits))
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*p++ = *string - '0';
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if (!seendot)
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tenpwr++;
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}
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} else {
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error (ERR_NONFATAL,
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"floating-point constant: `%c' is invalid character",
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*string);
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return;
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}
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string++;
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}
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if (*string) {
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string++; /* eat the E */
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tenpwr += atoi(string);
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}
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/*
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* At this point, the memory interval [digits,p) contains a
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* series of decimal digits zzzzzzz such that our number X
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* satisfies
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*
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* X = 0.zzzzzzz * 10^tenpwr
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*/
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bit = 0x8000;
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for (m=mant; m<mant+MANT_WORDS; m++)
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*m = 0;
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m = mant;
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q = digits;
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started = FALSE;
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twopwr = 0;
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while (m < mant+MANT_WORDS) {
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unsigned short carry = 0;
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while (p > q && !p[-1])
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p--;
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if (p <= q)
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break;
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for (r = p; r-- > q ;) {
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int i;
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i = 2 * *r + carry;
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if (i >= 10)
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carry = 1, i -= 10;
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else
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carry = 0;
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*r = i;
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}
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if (carry)
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*m |= bit, started = TRUE;
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if (started) {
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if (bit == 1)
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bit = 0x8000, m++;
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else
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bit >>= 1;
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} else
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twopwr--;
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}
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twopwr += tenpwr;
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/*
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* At this point the `mant' array contains the first six
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* fractional places of a base-2^16 real number, which when
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* multiplied by 2^twopwr and 5^tenpwr gives X. So now we
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* really do multiply by 5^tenpwr.
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*/
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if (tenpwr < 0) {
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for (m=mult; m<mult+MANT_WORDS; m++)
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*m = 0xCCCC;
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extratwos = -2;
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tenpwr = -tenpwr;
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} else if (tenpwr > 0) {
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mult[0] = 0xA000;
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for (m=mult+1; m<mult+MANT_WORDS; m++)
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*m = 0;
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extratwos = 3;
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} else
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extratwos = 0;
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while (tenpwr) {
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if (tenpwr & 1)
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twopwr += extratwos + ieee_multiply (mant, mult);
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extratwos = extratwos * 2 + ieee_multiply (mult, mult);
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tenpwr >>= 1;
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}
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/*
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* Conversion is done. The elements of `mant' contain the first
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* fractional places of a base-2^16 real number in [0.5,1)
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* which we can multiply by 2^twopwr to get X. Or, of course,
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* it contains zero.
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*/
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*exponent = twopwr;
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}
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/*
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* Shift a mantissa to the right by i (i < 16) bits.
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*/
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static void ieee_shr(unsigned short *mant, int i)
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{
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unsigned short n = 0, m;
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int j;
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for (j=0; j<MANT_WORDS; j++) {
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m = (mant[j] << (16-i)) & 0xFFFF;
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mant[j] = (mant[j] >> i) | n;
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n = m;
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}
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}
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/*
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* Round a mantissa off after i words.
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*/
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static int ieee_round(unsigned short *mant, int i)
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{
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if (mant[i] & 0x8000) {
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do {
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++mant[--i];
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mant[i] &= 0xFFFF;
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} while (i > 0 && !mant[i]);
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return !i && !mant[i];
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}
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return 0;
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}
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#define put(a,b) ( (*(a)=(b)), ((a)[1]=(b)>>8) )
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static int to_double(char *str, long sign, unsigned char *result,
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efunc error)
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{
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unsigned short mant[MANT_WORDS];
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long exponent;
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sign = (sign < 0 ? 0x8000L : 0L);
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ieee_flconvert (str, mant, &exponent, error);
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if (mant[0] & 0x8000) {
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/*
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* Non-zero.
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*/
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exponent--;
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if (exponent >= -1022 && exponent <= 1024) {
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/*
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* Normalised.
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*/
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exponent += 1023;
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ieee_shr(mant, 11);
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ieee_round(mant, 4);
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if (mant[0] & 0x20) /* did we scale up by one? */
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ieee_shr(mant, 1), exponent++;
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mant[0] &= 0xF; /* remove leading one */
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put(result+6,(exponent << 4) | mant[0] | sign);
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put(result+4,mant[1]);
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put(result+2,mant[2]);
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put(result+0,mant[3]);
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} else if (exponent < -1022 && exponent >= -1074) {
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/*
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* Denormal.
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*/
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int shift = -(exponent+1011);
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int sh = shift % 16, wds = shift / 16;
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ieee_shr(mant, sh);
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if (ieee_round(mant, 4-wds) || (sh>0 && (mant[0]&(0x8000>>(sh-1))))) {
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ieee_shr(mant, 1);
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if (sh==0)
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mant[0] |= 0x8000;
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exponent++;
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}
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put(result+6,(wds == 0 ? mant[0] : 0) | sign);
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put(result+4,(wds <= 1 ? mant[1-wds] : 0));
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put(result+2,(wds <= 2 ? mant[2-wds] : 0));
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put(result+0,(wds <= 3 ? mant[3-wds] : 0));
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} else {
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if (exponent > 0) {
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error(ERR_NONFATAL, "overflow in floating-point constant");
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return 0;
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} else
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memset (result, 0, 8);
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}
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} else {
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/*
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* Zero.
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*/
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memset (result, 0, 8);
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}
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return 1; /* success */
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}
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static int to_float(char *str, long sign, unsigned char *result,
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efunc error)
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{
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unsigned short mant[MANT_WORDS];
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long exponent;
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sign = (sign < 0 ? 0x8000L : 0L);
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ieee_flconvert (str, mant, &exponent, error);
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if (mant[0] & 0x8000) {
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/*
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* Non-zero.
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*/
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exponent--;
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if (exponent >= -126 && exponent <= 128) {
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/*
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* Normalised.
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*/
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exponent += 127;
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ieee_shr(mant, 8);
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ieee_round(mant, 2);
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if (mant[0] & 0x100) /* did we scale up by one? */
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ieee_shr(mant, 1), exponent++;
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mant[0] &= 0x7F; /* remove leading one */
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put(result+2,(exponent << 7) | mant[0] | sign);
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put(result+0,mant[1]);
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} else if (exponent < -126 && exponent >= -149) {
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/*
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* Denormal.
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*/
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int shift = -(exponent+118);
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int sh = shift % 16, wds = shift / 16;
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ieee_shr(mant, sh);
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if (ieee_round(mant, 2-wds) || (sh>0 && (mant[0]&(0x8000>>(sh-1))))) {
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ieee_shr(mant, 1);
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if (sh==0)
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mant[0] |= 0x8000;
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exponent++;
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}
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put(result+2,(wds == 0 ? mant[0] : 0) | sign);
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put(result+0,(wds <= 1 ? mant[1-wds] : 0));
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} else {
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if (exponent > 0) {
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error(ERR_NONFATAL, "overflow in floating-point constant");
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return 0;
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} else
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memset (result, 0, 4);
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}
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} else {
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memset (result, 0, 4);
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}
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return 1;
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}
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static int to_ldoub(char *str, long sign, unsigned char *result,
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efunc error)
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{
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unsigned short mant[MANT_WORDS];
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long exponent;
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sign = (sign < 0 ? 0x8000L : 0L);
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ieee_flconvert (str, mant, &exponent, error);
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if (mant[0] & 0x8000) {
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/*
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* Non-zero.
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*/
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exponent--;
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if (exponent >= -16383 && exponent <= 16384) {
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/*
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* Normalised.
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*/
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exponent += 16383;
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if (ieee_round(mant, 4)) /* did we scale up by one? */
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ieee_shr(mant, 1), mant[0] |= 0x8000, exponent++;
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put(result+8,exponent | sign);
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put(result+6,mant[0]);
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put(result+4,mant[1]);
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put(result+2,mant[2]);
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put(result+0,mant[3]);
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} else if (exponent < -16383 && exponent >= -16446) {
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/*
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* Denormal.
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*/
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int shift = -(exponent+16383);
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int sh = shift % 16, wds = shift / 16;
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ieee_shr(mant, sh);
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if (ieee_round(mant, 4-wds) || (sh>0 && (mant[0]&(0x8000>>(sh-1))))) {
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ieee_shr(mant, 1);
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if (sh==0)
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mant[0] |= 0x8000;
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exponent++;
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}
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put(result+8,sign);
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put(result+6,(wds == 0 ? mant[0] : 0));
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put(result+4,(wds <= 1 ? mant[1-wds] : 0));
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put(result+2,(wds <= 2 ? mant[2-wds] : 0));
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put(result+0,(wds <= 3 ? mant[3-wds] : 0));
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} else {
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if (exponent > 0) {
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error(ERR_NONFATAL, "overflow in floating-point constant");
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return 0;
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} else
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memset (result, 0, 10);
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}
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} else {
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/*
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* Zero.
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*/
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memset (result, 0, 10);
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}
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return 1;
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}
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int float_const (char *number, long sign, unsigned char *result, int bytes,
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efunc error)
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{
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if (bytes == 4)
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return to_float (number, sign, result, error);
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else if (bytes == 8)
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return to_double (number, sign, result, error);
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else if (bytes == 10)
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return to_ldoub (number, sign, result, error);
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else {
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error(ERR_PANIC, "strange value %d passed to float_const", bytes);
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return 0;
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}
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}
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