1 /* float.c floating-point constant support for the Netwide Assembler
3 * The Netwide Assembler is copyright (C) 1996 Simon Tatham and
4 * Julian Hall. All rights reserved. The software is
5 * redistributable under the licence given in the file "Licence"
6 * distributed in the NASM archive.
8 * initial version 13/ix/96 by Simon Tatham
22 #define MANT_WORDS 10 /* 112 bits + 48 for accuracy == 160 */
23 #define MANT_DIGITS 49 /* 50 digits don't fit in 160 bits */
26 * guaranteed top bit of from is set
27 * => we only have to worry about _one_ bit shift to the left
30 static int ieee_multiply(uint16_t *to, uint16_t *from)
32 uint32_t temp[MANT_WORDS * 2];
35 for (i = 0; i < MANT_WORDS * 2; i++)
38 for (i = 0; i < MANT_WORDS; i++)
39 for (j = 0; j < MANT_WORDS; j++) {
41 n = (uint32_t)to[i] * (uint32_t)from[j];
42 temp[i + j] += n >> 16;
43 temp[i + j + 1] += n & 0xFFFF;
46 for (i = MANT_WORDS * 2; --i;) {
47 temp[i - 1] += temp[i] >> 16;
50 if (temp[0] & 0x8000) {
51 memcpy(to, temp, 2*MANT_WORDS);
54 for (i = 0; i < MANT_WORDS; i++)
55 to[i] = (temp[i] << 1) + !!(temp[i + 1] & 0x8000);
60 static int hexval(char c)
62 if (c >= '0' && c <= '9')
64 else if (c >= 'a' && c <= 'f')
70 static void ieee_flconvert_hex(char *string, uint16_t *mant,
71 int32_t *exponent, efunc error)
73 static const int log2tbl[16] =
74 { -1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3 };
75 uint16_t mult[MANT_WORDS+1], *mp;
78 int seendot, seendigit;
82 seendot = seendigit = 0;
84 memset(mult, 0, sizeof mult);
86 while ((c = *string++) != '\0') {
92 "too many periods in floating-point constant");
95 } else if (isxdigit(c)) {
98 if (!seendigit && v) {
105 twopwr = seendot ? twopwr-4+l : l-3;
112 if (mp > &mult[MANT_WORDS])
113 mp = &mult[MANT_WORDS]; /* Guard slot */
125 } else if (c == 'p' || c == 'P') {
126 twopwr += atoi(string);
130 "floating-point constant: `%c' is invalid character",
137 memset(mant, 0, 2*MANT_WORDS); /* Zero */
140 memcpy(mant, mult, 2*MANT_WORDS);
145 static void ieee_flconvert(char *string, uint16_t *mant,
146 int32_t *exponent, efunc error)
148 char digits[MANT_DIGITS];
150 uint16_t mult[MANT_WORDS], bit;
152 int32_t tenpwr, twopwr;
153 int extratwos, started, seendot;
155 if (string[0] == '0' && (string[1] == 'x' || string[1] == 'X')) {
156 ieee_flconvert_hex(string+2, mant, exponent, error);
162 started = seendot = FALSE;
163 while (*string && *string != 'E' && *string != 'e') {
164 if (*string == '.') {
169 "too many periods in floating-point constant");
172 } else if (*string >= '0' && *string <= '9') {
173 if (*string == '0' && !started) {
178 if (p < digits + sizeof(digits))
179 *p++ = *string - '0';
185 "floating-point constant: `%c' is invalid character",
192 string++; /* eat the E */
193 tenpwr += atoi(string);
197 * At this point, the memory interval [digits,p) contains a
198 * series of decimal digits zzzzzzz such that our number X
201 * X = 0.zzzzzzz * 10^tenpwr
205 for (m = mant; m < mant + MANT_WORDS; m++)
211 while (m < mant + MANT_WORDS) {
213 while (p > q && !p[-1])
217 for (r = p; r-- > q;) {
228 *m |= bit, started = TRUE;
240 * At this point the `mant' array contains the first six
241 * fractional places of a base-2^16 real number, which when
242 * multiplied by 2^twopwr and 5^tenpwr gives X. So now we
243 * really do multiply by 5^tenpwr.
247 for (m = mult; m < mult + MANT_WORDS; m++)
251 } else if (tenpwr > 0) {
253 for (m = mult + 1; m < mult + MANT_WORDS; m++)
260 twopwr += extratwos + ieee_multiply(mant, mult);
261 extratwos = extratwos * 2 + ieee_multiply(mult, mult);
266 * Conversion is done. The elements of `mant' contain the first
267 * fractional places of a base-2^16 real number in [0.5,1)
268 * which we can multiply by 2^twopwr to get X. Or, of course,
275 * Shift a mantissa to the right by i (i < 16) bits.
277 static void ieee_shr(uint16_t *mant, int i)
282 for (j = 0; j < MANT_WORDS; j++) {
283 m = (mant[j] << (16 - i)) & 0xFFFF;
284 mant[j] = (mant[j] >> i) | n;
290 * Round a mantissa off after i words.
292 static int ieee_round(uint16_t *mant, int i)
294 if (mant[i] & 0x8000) {
298 } while (i > 0 && !mant[i]);
299 return !i && !mant[i];
304 #define put(a,b) ( (*(a)=(b)), ((a)[1]=(b)>>8) )
306 /* Produce standard IEEE formats, with implicit "1" bit; this makes
307 the following assumptions:
309 - the sign bit is the MSB, followed by the exponent.
310 - the sign bit plus exponent fit in 16 bits.
311 - the exponent bias is 2^(n-1)-1 for an n-bit exponent */
315 int mantissa; /* Bits in the mantissa */
316 int exponent; /* Bits in the exponent */
319 static const struct ieee_format ieee_16 = { 1, 10, 5 };
320 static const struct ieee_format ieee_32 = { 2, 23, 8 };
321 static const struct ieee_format ieee_64 = { 4, 52, 11 };
322 static const struct ieee_format ieee_128 = { 8, 112, 15 };
324 /* Produce all the standard IEEE formats: 16, 32, 64, and 128 bits */
325 static int to_float(char *str, int32_t sign, uint8_t *result,
326 const struct ieee_format *fmt, efunc error)
328 uint16_t mant[MANT_WORDS], *mp;
330 int32_t expmax = 1 << (fmt->exponent-1);
331 uint16_t implicit_one = 0x8000 >> fmt->exponent;
334 sign = (sign < 0 ? 0x8000L : 0L);
336 ieee_flconvert(str, mant, &exponent, error);
337 if (mant[0] & 0x8000) {
342 if (exponent >= 2-expmax && exponent <= expmax) {
347 ieee_shr(mant, fmt->exponent);
348 ieee_round(mant, fmt->words);
349 /* did we scale up by one? */
350 if (mant[0] & (implicit_one << 1)) {
355 mant[0] &= (implicit_one-1); /* remove leading one */
356 mant[0] |= exponent << (15 - fmt->exponent);
357 } else if (exponent < 2-expmax && exponent >= 2-expmax-fmt->mantissa) {
361 int shift = -(exponent + expmax-2-fmt->exponent);
362 int sh = shift % 16, wds = shift / 16;
364 if (ieee_round(mant, fmt->words - wds)
365 || (sh > 0 && (mant[0] & (0x8000 >> (sh - 1))))) {
373 for (i = fmt->words-1; i >= wds; i--)
374 mant[i] = mant[i-wds];
380 error(ERR_NONFATAL, "overflow in floating-point constant");
383 memset(mant, 0, 2*fmt->words);
388 memset(mant, 0, 2*fmt->words);
393 for (mp = &mant[fmt->words], i = 0; i < fmt->words; i++) {
399 return 1; /* success */
402 /* 80-bit format with 64-bit mantissa *including an explicit integer 1*
403 and 15-bit exponent. */
404 static int to_ldoub(char *str, int32_t sign, uint8_t *result,
407 uint16_t mant[MANT_WORDS];
410 sign = (sign < 0 ? 0x8000L : 0L);
412 ieee_flconvert(str, mant, &exponent, error);
413 if (mant[0] & 0x8000) {
418 if (exponent >= -16383 && exponent <= 16384) {
423 if (ieee_round(mant, 4)) /* did we scale up by one? */
424 ieee_shr(mant, 1), mant[0] |= 0x8000, exponent++;
425 put(result + 8, exponent | sign);
426 put(result + 6, mant[0]);
427 put(result + 4, mant[1]);
428 put(result + 2, mant[2]);
429 put(result + 0, mant[3]);
430 } else if (exponent < -16383 && exponent >= -16446) {
434 int shift = -(exponent + 16383);
435 int sh = shift % 16, wds = shift / 16;
437 if (ieee_round(mant, 4 - wds)
438 || (sh > 0 && (mant[0] & (0x8000 >> (sh - 1))))) {
444 put(result + 8, sign);
445 put(result + 6, (wds == 0 ? mant[0] : 0));
446 put(result + 4, (wds <= 1 ? mant[1 - wds] : 0));
447 put(result + 2, (wds <= 2 ? mant[2 - wds] : 0));
448 put(result + 0, (wds <= 3 ? mant[3 - wds] : 0));
451 error(ERR_NONFATAL, "overflow in floating-point constant");
454 memset(result, 0, 10);
460 memset(result, 0, 10);
465 int float_const(char *number, int32_t sign, uint8_t *result, int bytes,
470 return to_float(number, sign, result, &ieee_16, error);
472 return to_float(number, sign, result, &ieee_32, error);
474 return to_float(number, sign, result, &ieee_64, error);
476 return to_ldoub(number, sign, result, error);
478 return to_float(number, sign, result, &ieee_128, error);
480 error(ERR_PANIC, "strange value %d passed to float_const", bytes);