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
28 static bool daz = false; /* denormals as zero */
29 static enum float_round rc = FLOAT_RC_NEAR; /* rounding control */
37 /* 112 bits + 64 bits for accuracy + 16 bits for rounding */
40 /* 52 digits fit in 176 bits because 10^53 > 2^176 > 10^52 */
41 #define MANT_DIGITS 52
43 /* the format and the argument list depend on MANT_WORDS */
44 #define MANT_FMT "%04x%04x_%04x%04x_%04x%04x_%04x%04x_%04x%04x_%04x%04x"
45 #define MANT_ARG SOME_ARG(mant, 0)
47 #define SOME_ARG(a,i) (a)[(i)+0], (a)[(i)+1], (a)[(i)+2], (a)[(i)+3], \
48 (a)[(i)+4], (a)[(i)+5], (a)[(i)+6], (a)[(i)+7], (a)[(i)+8], \
49 (a)[(i)+9], (a)[(i)+10], (a)[(i)+11]
52 * ---------------------------------------------------------------------------
53 * emit a printf()-like debug message... but only if DEBUG_FLOAT was defined
54 * ---------------------------------------------------------------------------
58 #define dprintf(x) printf x
60 #define dprintf(x) do { } while (0)
64 * ---------------------------------------------------------------------------
66 * ---------------------------------------------------------------------------
68 static int float_multiply(uint16_t * to, uint16_t * from)
70 uint32_t temp[MANT_WORDS * 2];
74 * guaranteed that top bit of 'from' is set -- so we only have
75 * to worry about _one_ bit shift to the left
77 dprintf(("%s=" MANT_FMT "\n", "mul1", SOME_ARG(to, 0)));
78 dprintf(("%s=" MANT_FMT "\n", "mul2", SOME_ARG(from, 0)));
80 memset(temp, 0, sizeof temp);
82 for (i = 0; i < MANT_WORDS; i++) {
83 for (j = 0; j < MANT_WORDS; j++) {
85 n = (uint32_t) to[i] * (uint32_t) from[j];
86 temp[i + j] += n >> 16;
87 temp[i + j + 1] += n & 0xFFFF;
91 for (i = MANT_WORDS * 2; --i;) {
92 temp[i - 1] += temp[i] >> 16;
96 dprintf(("%s=" MANT_FMT "_" MANT_FMT "\n", "temp", SOME_ARG(temp, 0),
97 SOME_ARG(temp, MANT_WORDS)));
99 if (temp[0] & 0x8000) {
100 for (i = 0; i < MANT_WORDS; i++) {
101 to[i] = temp[i] & 0xFFFF;
103 dprintf(("%s=" MANT_FMT " (%i)\n", "prod", SOME_ARG(to, 0), 0));
106 for (i = 0; i < MANT_WORDS; i++) {
107 to[i] = (temp[i] << 1) + !!(temp[i + 1] & 0x8000);
109 dprintf(("%s=" MANT_FMT " (%i)\n", "prod", SOME_ARG(to, 0), -1));
115 * ---------------------------------------------------------------------------
117 * ---------------------------------------------------------------------------
119 static bool ieee_flconvert(const char *string, uint16_t * mant,
122 char digits[MANT_DIGITS];
124 uint16_t mult[MANT_WORDS], bit;
126 int32_t tenpwr, twopwr;
128 bool started, seendot, warned;
131 started = seendot = warned = false;
132 while (*string && *string != 'E' && *string != 'e') {
133 if (*string == '.') {
138 "too many periods in floating-point constant");
141 } else if (*string >= '0' && *string <= '9') {
142 if (*string == '0' && !started) {
148 if (p < digits + sizeof(digits)) {
149 *p++ = *string - '0';
153 "floating-point constant significand contains "
154 "more than %i digits", MANT_DIGITS);
162 } else if (*string == '_') {
167 "invalid character in floating-point constant %s: '%c'",
168 "significand", *string);
176 string++; /* eat the E */
177 if (*string == '+') {
179 } else if (*string == '-') {
184 if (*string >= '0' && *string <= '9') {
185 i = (i * 10) + (*string - '0');
188 * To ensure that underflows and overflows are
189 * handled properly we must avoid wraparounds of
190 * the signed integer value that is used to hold
191 * the exponent. Therefore we cap the exponent at
192 * +/-5000, which is slightly more/less than
193 * what's required for normal and denormal numbers
194 * in single, double, and extended precision, but
195 * sufficient to avoid signed integer wraparound.
200 } else if (*string == '_') {
205 "invalid character in floating-point constant %s: '%c'",
206 "exponent", *string);
218 * At this point, the memory interval [digits,p) contains a
219 * series of decimal digits zzzzzzz, such that our number X
220 * satisfies X = 0.zzzzzzz * 10^tenpwr.
225 dprintf(("%c", *q + '0'));
228 dprintf((" * 10^%i\n", tenpwr));
231 * Now convert [digits,p) to our internal representation.
234 for (m = mant; m < mant + MANT_WORDS; m++) {
241 while (m < mant + MANT_WORDS) {
243 while (p > q && !p[-1]) {
249 for (r = p; r-- > q;) {
278 * At this point, the 'mant' array contains the first frac-
279 * tional places of a base-2^16 real number which when mul-
280 * tiplied by 2^twopwr and 5^tenpwr gives X.
282 dprintf(("X = " MANT_FMT " * 2^%i * 5^%i\n", MANT_ARG, twopwr,
286 * Now multiply 'mant' by 5^tenpwr.
288 if (tenpwr < 0) { /* mult = 5^-1 = 0.2 */
289 for (m = mult; m < mult + MANT_WORDS - 1; m++) {
292 mult[MANT_WORDS - 1] = 0xCCCD;
297 * If tenpwr was 1000...000b, then it becomes 1000...000b. See
298 * the "ANSI C" comment below for more details on that case.
300 * Because we already truncated tenpwr to +5000...-5000 inside
301 * the exponent parsing code, this shouldn't happen though.
303 } else if (tenpwr > 0) { /* mult = 5^+1 = 5.0 */
305 for (m = mult + 1; m < mult + MANT_WORDS; m++) {
313 dprintf(("loop=" MANT_FMT " * 2^%i * 5^%i (%i)\n", MANT_ARG,
314 twopwr, tenpwr, extratwos));
316 dprintf(("mant*mult\n"));
317 twopwr += extratwos + float_multiply(mant, mult);
319 dprintf(("mult*mult\n"));
320 extratwos = extratwos * 2 + float_multiply(mult, mult);
324 * In ANSI C, the result of right-shifting a signed integer is
325 * considered implementation-specific. To ensure that the loop
326 * terminates even if tenpwr was 1000...000b to begin with, we
327 * manually clear the MSB, in case a 1 was shifted in.
329 * Because we already truncated tenpwr to +5000...-5000 inside
330 * the exponent parsing code, this shouldn't matter; neverthe-
331 * less it is the right thing to do here.
333 tenpwr &= (uint32_t) - 1 >> 1;
337 * At this point, the 'mant' array contains the first frac-
338 * tional places of a base-2^16 real number in [0.5,1) that
339 * when multiplied by 2^twopwr gives X. Or it contains zero
340 * of course. We are done.
347 * ---------------------------------------------------------------------------
348 * round a mantissa off after i words
349 * ---------------------------------------------------------------------------
352 #define ROUND_COLLECT_BITS \
353 for (j = i; j < MANT_WORDS; j++) { \
357 #define ROUND_ABS_DOWN \
358 for (j = i; j < MANT_WORDS; j++) { \
362 #define ROUND_ABS_UP \
366 } while (i > 0 && !mant[i]); \
367 return (!i && !mant[i]);
369 static int32_t ieee_round(int sign, uint16_t * mant, int32_t i)
373 if ((sign == 0x0000) || (sign == 0x8000)) {
374 if (rc == FLOAT_RC_NEAR) {
375 if (mant[i] & 0x8000) {
382 if (mant[i - 1] & 1) {
391 } else if (((sign == 0x0000) && (rc == FLOAT_RC_DOWN))
392 || ((sign == 0x8000) && (rc == FLOAT_RC_UP))) {
397 } else if (((sign == 0x0000) && (rc == FLOAT_RC_UP))
398 || ((sign == 0x8000) && (rc == FLOAT_RC_DOWN))) {
403 } else if (rc == FLOAT_RC_ZERO) {
406 error(ERR_PANIC, "float_round() can't handle rc=%i", rc);
409 error(ERR_PANIC, "float_round() can't handle sign=%i", sign);
414 static int hexval(char c)
416 if (c >= '0' && c <= '9')
418 else if (c >= 'a' && c <= 'f')
424 static void ieee_flconvert_hex(const char *string, uint16_t * mant,
427 static const int log2tbl[16] =
428 { -1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3 };
429 uint16_t mult[MANT_WORDS + 1], *mp;
432 int seendot, seendigit;
436 seendot = seendigit = 0;
440 memset(mult, 0, sizeof mult);
442 while ((c = *string++) != '\0') {
448 "too many periods in floating-point constant");
451 } else if (isxdigit(c)) {
454 if (!seendigit && v) {
461 twopwr = seendot ? twopwr - 4 + l : l - 3;
468 if (mp > &mult[MANT_WORDS])
469 mp = &mult[MANT_WORDS]; /* Guard slot */
481 } else if (c == 'p' || c == 'P') {
482 twopwr += atoi(string);
486 "floating-point constant: `%c' is invalid character", c);
492 memset(mant, 0, 2 * MANT_WORDS); /* Zero */
495 memcpy(mant, mult, 2 * MANT_WORDS);
501 * Shift a mantissa to the right by i (i < 16) bits.
503 static void ieee_shr(uint16_t * mant, int i)
508 for (j = 0; j < MANT_WORDS; j++) {
509 m = (mant[j] << (16 - i)) & 0xFFFF;
510 mant[j] = (mant[j] >> i) | n;
515 #if defined(__i386__) || defined(__x86_64__)
516 #define put(a,b) (*(uint16_t *)(a) = (b))
518 #define put(a,b) (((a)[0] = (b)), ((a)[1] = (b) >> 8))
521 /* Set a bit, using *bigendian* bit numbering (0 = MSB) */
522 static void set_bit(uint16_t * mant, int bit)
524 mant[bit >> 4] |= 1 << (~bit & 15);
527 /* Produce standard IEEE formats, with implicit "1" bit; this makes
528 the following assumptions:
530 - the sign bit is the MSB, followed by the exponent.
531 - the sign bit plus exponent fit in 16 bits.
532 - the exponent bias is 2^(n-1)-1 for an n-bit exponent */
536 int mantissa; /* Bits in the mantissa */
537 int exponent; /* Bits in the exponent */
540 static const struct ieee_format ieee_16 = { 1, 10, 5 };
541 static const struct ieee_format ieee_32 = { 2, 23, 8 };
542 static const struct ieee_format ieee_64 = { 4, 52, 11 };
543 static const struct ieee_format ieee_128 = { 8, 112, 15 };
545 /* Produce all the standard IEEE formats: 16, 32, 64, and 128 bits */
546 static int to_float(const char *str, int sign, uint8_t * result,
547 const struct ieee_format *fmt)
549 uint16_t mant[MANT_WORDS], *mp;
551 int32_t expmax = 1 << (fmt->exponent - 1);
552 uint16_t implicit_one = 0x8000 >> fmt->exponent;
555 sign = (sign < 0 ? 0x8000L : 0L);
558 /* NaN or Infinity */
559 int32_t expmask = (1 << fmt->exponent) - 1;
561 memset(mant, 0, sizeof mant);
562 mant[0] = expmask << (15 - fmt->exponent); /* Exponent: all bits one */
565 case 'n': /* __nan__ */
567 case 'q': /* __qnan__ */
569 set_bit(mant, fmt->exponent + 1); /* Highest bit in mantissa */
571 case 's': /* __snan__ */
573 set_bit(mant, fmt->exponent + fmt->mantissa); /* Last bit */
575 case 'i': /* __infinity__ */
580 if (str[0] == '0' && (str[1] == 'x' || str[1] == 'X'))
581 ieee_flconvert_hex(str + 2, mant, &exponent);
583 ieee_flconvert(str, mant, &exponent);
585 if (mant[0] & 0x8000) {
590 if (exponent >= 2 - expmax && exponent <= expmax) {
594 exponent += expmax - 1;
595 ieee_shr(mant, fmt->exponent);
596 ieee_round(sign, mant, fmt->words);
597 /* did we scale up by one? */
598 if (mant[0] & (implicit_one << 1)) {
603 mant[0] &= (implicit_one - 1); /* remove leading one */
604 mant[0] |= exponent << (15 - fmt->exponent);
605 } else if (!daz && exponent < 2 - expmax &&
606 exponent >= 2 - expmax - fmt->mantissa) {
610 int shift = -(exponent + expmax - 2 - fmt->exponent);
611 int sh = shift % 16, wds = shift / 16;
613 if (ieee_round(sign, mant, fmt->words - wds)
614 || (sh > 0 && (mant[0] & (0x8000 >> (sh - 1))))) {
622 for (i = fmt->words - 1; i >= wds; i--)
623 mant[i] = mant[i - wds];
630 "overflow in floating-point constant");
631 /* We should generate Inf here */
634 memset(mant, 0, 2 * fmt->words);
639 memset(mant, 0, 2 * fmt->words);
645 for (mp = &mant[fmt->words], i = 0; i < fmt->words; i++) {
651 return 1; /* success */
654 /* 80-bit format with 64-bit mantissa *including an explicit integer 1*
655 and 15-bit exponent. */
656 static int to_ldoub(const char *str, int sign, uint8_t * result)
658 uint16_t mant[MANT_WORDS];
661 sign = (sign < 0 ? 0x8000L : 0L);
664 uint16_t is_snan = 0, is_qnan = 0x8000;
680 put(result + 0, is_snan);
683 put(result + 6, is_qnan);
684 put(result + 8, 0x7fff | sign);
688 if (str[0] == '0' && (str[1] == 'x' || str[1] == 'X'))
689 ieee_flconvert_hex(str + 2, mant, &exponent);
691 ieee_flconvert(str, mant, &exponent);
693 if (mant[0] & 0x8000) {
698 if (exponent >= -16383 && exponent <= 16384) {
703 if (ieee_round(sign, mant, 4)) /* did we scale up by one? */
704 ieee_shr(mant, 1), mant[0] |= 0x8000, exponent++;
705 put(result + 0, mant[3]);
706 put(result + 2, mant[2]);
707 put(result + 4, mant[1]);
708 put(result + 6, mant[0]);
709 put(result + 8, exponent | sign);
710 } else if (!daz && exponent < -16383 && exponent >= -16446) {
714 int shift = -(exponent + 16383);
715 int sh = shift % 16, wds = shift / 16;
717 if (ieee_round(sign, mant, 4 - wds)
718 || (sh > 0 && (mant[0] & (0x8000 >> (sh - 1))))) {
724 put(result + 0, (wds <= 3 ? mant[3 - wds] : 0));
725 put(result + 2, (wds <= 2 ? mant[2 - wds] : 0));
726 put(result + 4, (wds <= 1 ? mant[1 - wds] : 0));
727 put(result + 6, (wds == 0 ? mant[0] : 0));
728 put(result + 8, sign);
731 error(ERR_NONFATAL, "overflow in floating-point constant");
732 /* We should generate Inf here */
747 put(result + 8, sign);
752 int float_const(const char *number, int32_t sign, uint8_t * result,
753 int bytes, efunc err)
759 return to_float(number, sign, result, &ieee_16);
761 return to_float(number, sign, result, &ieee_32);
763 return to_float(number, sign, result, &ieee_64);
765 return to_ldoub(number, sign, result);
767 return to_float(number, sign, result, &ieee_128);
769 error(ERR_PANIC, "strange value %d passed to float_const", bytes);