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Diffstat (limited to 'REORG.TODO/sysdeps/ieee754/ldbl-128/s_fmal.c')
| -rw-r--r-- | REORG.TODO/sysdeps/ieee754/ldbl-128/s_fmal.c | 298 |
1 files changed, 298 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/ieee754/ldbl-128/s_fmal.c b/REORG.TODO/sysdeps/ieee754/ldbl-128/s_fmal.c new file mode 100644 index 0000000000..40c4e73d2b --- /dev/null +++ b/REORG.TODO/sysdeps/ieee754/ldbl-128/s_fmal.c @@ -0,0 +1,298 @@ +/* Compute x * y + z as ternary operation. + Copyright (C) 2010-2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Jakub Jelinek <jakub@redhat.com>, 2010. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <float.h> +#include <math.h> +#include <fenv.h> +#include <ieee754.h> +#include <math_private.h> +#include <tininess.h> + +/* This implementation uses rounding to odd to avoid problems with + double rounding. See a paper by Boldo and Melquiond: + http://www.lri.fr/~melquion/doc/08-tc.pdf */ + +_Float128 +__fmal (_Float128 x, _Float128 y, _Float128 z) +{ + union ieee854_long_double u, v, w; + int adjust = 0; + u.d = x; + v.d = y; + w.d = z; + if (__builtin_expect (u.ieee.exponent + v.ieee.exponent + >= 0x7fff + IEEE854_LONG_DOUBLE_BIAS + - LDBL_MANT_DIG, 0) + || __builtin_expect (u.ieee.exponent >= 0x7fff - LDBL_MANT_DIG, 0) + || __builtin_expect (v.ieee.exponent >= 0x7fff - LDBL_MANT_DIG, 0) + || __builtin_expect (w.ieee.exponent >= 0x7fff - LDBL_MANT_DIG, 0) + || __builtin_expect (u.ieee.exponent + v.ieee.exponent + <= IEEE854_LONG_DOUBLE_BIAS + LDBL_MANT_DIG, 0)) + { + /* If z is Inf, but x and y are finite, the result should be + z rather than NaN. */ + if (w.ieee.exponent == 0x7fff + && u.ieee.exponent != 0x7fff + && v.ieee.exponent != 0x7fff) + return (z + x) + y; + /* If z is zero and x are y are nonzero, compute the result + as x * y to avoid the wrong sign of a zero result if x * y + underflows to 0. */ + if (z == 0 && x != 0 && y != 0) + return x * y; + /* If x or y or z is Inf/NaN, or if x * y is zero, compute as + x * y + z. */ + if (u.ieee.exponent == 0x7fff + || v.ieee.exponent == 0x7fff + || w.ieee.exponent == 0x7fff + || x == 0 + || y == 0) + return x * y + z; + /* If fma will certainly overflow, compute as x * y. */ + if (u.ieee.exponent + v.ieee.exponent + > 0x7fff + IEEE854_LONG_DOUBLE_BIAS) + return x * y; + /* If x * y is less than 1/4 of LDBL_TRUE_MIN, neither the + result nor whether there is underflow depends on its exact + value, only on its sign. */ + if (u.ieee.exponent + v.ieee.exponent + < IEEE854_LONG_DOUBLE_BIAS - LDBL_MANT_DIG - 2) + { + int neg = u.ieee.negative ^ v.ieee.negative; + _Float128 tiny = neg ? L(-0x1p-16494) : L(0x1p-16494); + if (w.ieee.exponent >= 3) + return tiny + z; + /* Scaling up, adding TINY and scaling down produces the + correct result, because in round-to-nearest mode adding + TINY has no effect and in other modes double rounding is + harmless. But it may not produce required underflow + exceptions. */ + v.d = z * L(0x1p114) + tiny; + if (TININESS_AFTER_ROUNDING + ? v.ieee.exponent < 115 + : (w.ieee.exponent == 0 + || (w.ieee.exponent == 1 + && w.ieee.negative != neg + && w.ieee.mantissa3 == 0 + && w.ieee.mantissa2 == 0 + && w.ieee.mantissa1 == 0 + && w.ieee.mantissa0 == 0))) + { + _Float128 force_underflow = x * y; + math_force_eval (force_underflow); + } + return v.d * L(0x1p-114); + } + if (u.ieee.exponent + v.ieee.exponent + >= 0x7fff + IEEE854_LONG_DOUBLE_BIAS - LDBL_MANT_DIG) + { + /* Compute 1p-113 times smaller result and multiply + at the end. */ + if (u.ieee.exponent > v.ieee.exponent) + u.ieee.exponent -= LDBL_MANT_DIG; + else + v.ieee.exponent -= LDBL_MANT_DIG; + /* If x + y exponent is very large and z exponent is very small, + it doesn't matter if we don't adjust it. */ + if (w.ieee.exponent > LDBL_MANT_DIG) + w.ieee.exponent -= LDBL_MANT_DIG; + adjust = 1; + } + else if (w.ieee.exponent >= 0x7fff - LDBL_MANT_DIG) + { + /* Similarly. + If z exponent is very large and x and y exponents are + very small, adjust them up to avoid spurious underflows, + rather than down. */ + if (u.ieee.exponent + v.ieee.exponent + <= IEEE854_LONG_DOUBLE_BIAS + 2 * LDBL_MANT_DIG) + { + if (u.ieee.exponent > v.ieee.exponent) + u.ieee.exponent += 2 * LDBL_MANT_DIG + 2; + else + v.ieee.exponent += 2 * LDBL_MANT_DIG + 2; + } + else if (u.ieee.exponent > v.ieee.exponent) + { + if (u.ieee.exponent > LDBL_MANT_DIG) + u.ieee.exponent -= LDBL_MANT_DIG; + } + else if (v.ieee.exponent > LDBL_MANT_DIG) + v.ieee.exponent -= LDBL_MANT_DIG; + w.ieee.exponent -= LDBL_MANT_DIG; + adjust = 1; + } + else if (u.ieee.exponent >= 0x7fff - LDBL_MANT_DIG) + { + u.ieee.exponent -= LDBL_MANT_DIG; + if (v.ieee.exponent) + v.ieee.exponent += LDBL_MANT_DIG; + else + v.d *= L(0x1p113); + } + else if (v.ieee.exponent >= 0x7fff - LDBL_MANT_DIG) + { + v.ieee.exponent -= LDBL_MANT_DIG; + if (u.ieee.exponent) + u.ieee.exponent += LDBL_MANT_DIG; + else + u.d *= L(0x1p113); + } + else /* if (u.ieee.exponent + v.ieee.exponent + <= IEEE854_LONG_DOUBLE_BIAS + LDBL_MANT_DIG) */ + { + if (u.ieee.exponent > v.ieee.exponent) + u.ieee.exponent += 2 * LDBL_MANT_DIG + 2; + else + v.ieee.exponent += 2 * LDBL_MANT_DIG + 2; + if (w.ieee.exponent <= 4 * LDBL_MANT_DIG + 6) + { + if (w.ieee.exponent) + w.ieee.exponent += 2 * LDBL_MANT_DIG + 2; + else + w.d *= L(0x1p228); + adjust = -1; + } + /* Otherwise x * y should just affect inexact + and nothing else. */ + } + x = u.d; + y = v.d; + z = w.d; + } + + /* Ensure correct sign of exact 0 + 0. */ + if (__glibc_unlikely ((x == 0 || y == 0) && z == 0)) + { + x = math_opt_barrier (x); + return x * y + z; + } + + fenv_t env; + feholdexcept (&env); + fesetround (FE_TONEAREST); + + /* Multiplication m1 + m2 = x * y using Dekker's algorithm. */ +#define C ((1LL << (LDBL_MANT_DIG + 1) / 2) + 1) + _Float128 x1 = x * C; + _Float128 y1 = y * C; + _Float128 m1 = x * y; + x1 = (x - x1) + x1; + y1 = (y - y1) + y1; + _Float128 x2 = x - x1; + _Float128 y2 = y - y1; + _Float128 m2 = (((x1 * y1 - m1) + x1 * y2) + x2 * y1) + x2 * y2; + + /* Addition a1 + a2 = z + m1 using Knuth's algorithm. */ + _Float128 a1 = z + m1; + _Float128 t1 = a1 - z; + _Float128 t2 = a1 - t1; + t1 = m1 - t1; + t2 = z - t2; + _Float128 a2 = t1 + t2; + /* Ensure the arithmetic is not scheduled after feclearexcept call. */ + math_force_eval (m2); + math_force_eval (a2); + feclearexcept (FE_INEXACT); + + /* If the result is an exact zero, ensure it has the correct sign. */ + if (a1 == 0 && m2 == 0) + { + feupdateenv (&env); + /* Ensure that round-to-nearest value of z + m1 is not reused. */ + z = math_opt_barrier (z); + return z + m1; + } + + fesetround (FE_TOWARDZERO); + /* Perform m2 + a2 addition with round to odd. */ + u.d = a2 + m2; + + if (__glibc_likely (adjust == 0)) + { + if ((u.ieee.mantissa3 & 1) == 0 && u.ieee.exponent != 0x7fff) + u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0; + feupdateenv (&env); + /* Result is a1 + u.d. */ + return a1 + u.d; + } + else if (__glibc_likely (adjust > 0)) + { + if ((u.ieee.mantissa3 & 1) == 0 && u.ieee.exponent != 0x7fff) + u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0; + feupdateenv (&env); + /* Result is a1 + u.d, scaled up. */ + return (a1 + u.d) * L(0x1p113); + } + else + { + if ((u.ieee.mantissa3 & 1) == 0) + u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0; + v.d = a1 + u.d; + /* Ensure the addition is not scheduled after fetestexcept call. */ + math_force_eval (v.d); + int j = fetestexcept (FE_INEXACT) != 0; + feupdateenv (&env); + /* Ensure the following computations are performed in default rounding + mode instead of just reusing the round to zero computation. */ + asm volatile ("" : "=m" (u) : "m" (u)); + /* If a1 + u.d is exact, the only rounding happens during + scaling down. */ + if (j == 0) + return v.d * L(0x1p-228); + /* If result rounded to zero is not subnormal, no double + rounding will occur. */ + if (v.ieee.exponent > 228) + return (a1 + u.d) * L(0x1p-228); + /* If v.d * 0x1p-228L with round to zero is a subnormal above + or equal to LDBL_MIN / 2, then v.d * 0x1p-228L shifts mantissa + down just by 1 bit, which means v.ieee.mantissa3 |= j would + change the round bit, not sticky or guard bit. + v.d * 0x1p-228L never normalizes by shifting up, + so round bit plus sticky bit should be already enough + for proper rounding. */ + if (v.ieee.exponent == 228) + { + /* If the exponent would be in the normal range when + rounding to normal precision with unbounded exponent + range, the exact result is known and spurious underflows + must be avoided on systems detecting tininess after + rounding. */ + if (TININESS_AFTER_ROUNDING) + { + w.d = a1 + u.d; + if (w.ieee.exponent == 229) + return w.d * L(0x1p-228); + } + /* v.ieee.mantissa3 & 2 is LSB bit of the result before rounding, + v.ieee.mantissa3 & 1 is the round bit and j is our sticky + bit. */ + w.d = 0; + w.ieee.mantissa3 = ((v.ieee.mantissa3 & 3) << 1) | j; + w.ieee.negative = v.ieee.negative; + v.ieee.mantissa3 &= ~3U; + v.d *= L(0x1p-228); + w.d *= L(0x1p-2); + return v.d + w.d; + } + v.ieee.mantissa3 |= j; + return v.d * L(0x1p-228); + } +} +weak_alias (__fmal, fmal) |