gcc/libquadmath/math/fmaq.c
Joseph Myers 667b3ec15d Update libquadmath fmaq from glibc, fix nanq issues.
This patch extends update-quadmath.py to update fmaq from glibc.

The issue in that function was that quadmath-imp.h had a struct in a
union with mant_high and mant_low fields (up to 64-bit) whereas glibc
has mantissa0, mantissa1, mantissa2 and mantissa3 (up to 32-bit).  The
patch changes those fields to be the same as in glibc, moving printf /
strtod code that also uses those fields back to closer to the glibc
form.  This allows fmaq to be updated automatically from glibc (which
brings in at least one bug fix from glibc from 2015).

nanq was also using the mant_high field name, and had other issues: it
only partly initialized the union from which a value was returned, and
setting mant_high to 1 meant a signaling NaN would be returned rather
than a quiet NaN.  This patch fixes those issues as part of updating
it to use the changed interfaces (but does not fix the issue of not
using the argument).

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

	* quadmath-imp.h (ieee854_float128): Use mantissa0, mantissa1,
	mantissa2 and mantissa3 fields instead of mant_high and mant_low.
	Change nan field to ieee_nan.
	* update-quadmath.py (update_sources): Also update fmaq.c.
	* math/nanq.c (nanq): Use ieee_nan field of union.
	Zero-initialize f.  Set quiet_nan field.
	* printf/flt1282mpn.c, printf/printf_fphex.c, strtod/mpn2flt128.c,
	strtod/strtoflt128.c: Use mantissa0, mantissa1, mantissa2 and
	mantissa3 fields.  Use ieee_nan and quiet_nan field.
	* math/fmaq.c: Regenerate from glibc sources with
	update-quadmath.py.

From-SVN: r265874
2018-11-07 13:49:03 +00:00

293 lines
9.7 KiB
C

/* Compute x * y + z as ternary operation.
Copyright (C) 2010-2018 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 "quadmath-imp.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
fmaq (__float128 x, __float128 y, __float128 z)
{
ieee854_float128 u, v, w;
int adjust = 0;
u.value = x;
v.value = y;
w.value = z;
if (__builtin_expect (u.ieee.exponent + v.ieee.exponent
>= 0x7fff + IEEE854_FLOAT128_BIAS
- FLT128_MANT_DIG, 0)
|| __builtin_expect (u.ieee.exponent >= 0x7fff - FLT128_MANT_DIG, 0)
|| __builtin_expect (v.ieee.exponent >= 0x7fff - FLT128_MANT_DIG, 0)
|| __builtin_expect (w.ieee.exponent >= 0x7fff - FLT128_MANT_DIG, 0)
|| __builtin_expect (u.ieee.exponent + v.ieee.exponent
<= IEEE854_FLOAT128_BIAS + FLT128_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_FLOAT128_BIAS)
return x * y;
/* If x * y is less than 1/4 of FLT128_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_FLOAT128_BIAS - FLT128_MANT_DIG - 2)
{
int neg = u.ieee.negative ^ v.ieee.negative;
__float128 tiny = neg ? -0x1p-16494Q : 0x1p-16494Q;
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.value = z * 0x1p114Q + 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.value * 0x1p-114Q;
}
if (u.ieee.exponent + v.ieee.exponent
>= 0x7fff + IEEE854_FLOAT128_BIAS - FLT128_MANT_DIG)
{
/* Compute 1p-113 times smaller result and multiply
at the end. */
if (u.ieee.exponent > v.ieee.exponent)
u.ieee.exponent -= FLT128_MANT_DIG;
else
v.ieee.exponent -= FLT128_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 > FLT128_MANT_DIG)
w.ieee.exponent -= FLT128_MANT_DIG;
adjust = 1;
}
else if (w.ieee.exponent >= 0x7fff - FLT128_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_FLOAT128_BIAS + 2 * FLT128_MANT_DIG)
{
if (u.ieee.exponent > v.ieee.exponent)
u.ieee.exponent += 2 * FLT128_MANT_DIG + 2;
else
v.ieee.exponent += 2 * FLT128_MANT_DIG + 2;
}
else if (u.ieee.exponent > v.ieee.exponent)
{
if (u.ieee.exponent > FLT128_MANT_DIG)
u.ieee.exponent -= FLT128_MANT_DIG;
}
else if (v.ieee.exponent > FLT128_MANT_DIG)
v.ieee.exponent -= FLT128_MANT_DIG;
w.ieee.exponent -= FLT128_MANT_DIG;
adjust = 1;
}
else if (u.ieee.exponent >= 0x7fff - FLT128_MANT_DIG)
{
u.ieee.exponent -= FLT128_MANT_DIG;
if (v.ieee.exponent)
v.ieee.exponent += FLT128_MANT_DIG;
else
v.value *= 0x1p113Q;
}
else if (v.ieee.exponent >= 0x7fff - FLT128_MANT_DIG)
{
v.ieee.exponent -= FLT128_MANT_DIG;
if (u.ieee.exponent)
u.ieee.exponent += FLT128_MANT_DIG;
else
u.value *= 0x1p113Q;
}
else /* if (u.ieee.exponent + v.ieee.exponent
<= IEEE854_FLOAT128_BIAS + FLT128_MANT_DIG) */
{
if (u.ieee.exponent > v.ieee.exponent)
u.ieee.exponent += 2 * FLT128_MANT_DIG + 2;
else
v.ieee.exponent += 2 * FLT128_MANT_DIG + 2;
if (w.ieee.exponent <= 4 * FLT128_MANT_DIG + 6)
{
if (w.ieee.exponent)
w.ieee.exponent += 2 * FLT128_MANT_DIG + 2;
else
w.value *= 0x1p228Q;
adjust = -1;
}
/* Otherwise x * y should just affect inexact
and nothing else. */
}
x = u.value;
y = v.value;
z = w.value;
}
/* 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 << (FLT128_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.value = 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.value. */
return a1 + u.value;
}
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.value, scaled up. */
return (a1 + u.value) * 0x1p113Q;
}
else
{
if ((u.ieee.mantissa3 & 1) == 0)
u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0;
v.value = a1 + u.value;
/* Ensure the addition is not scheduled after fetestexcept call. */
math_force_eval (v.value);
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.value is exact, the only rounding happens during
scaling down. */
if (j == 0)
return v.value * 0x1p-228Q;
/* If result rounded to zero is not subnormal, no double
rounding will occur. */
if (v.ieee.exponent > 228)
return (a1 + u.value) * 0x1p-228Q;
/* If v.value * 0x1p-228L with round to zero is a subnormal above
or equal to FLT128_MIN / 2, then v.value * 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.value * 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.value = a1 + u.value;
if (w.ieee.exponent == 229)
return w.value * 0x1p-228Q;
}
/* 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.value = 0;
w.ieee.mantissa3 = ((v.ieee.mantissa3 & 3) << 1) | j;
w.ieee.negative = v.ieee.negative;
v.ieee.mantissa3 &= ~3U;
v.value *= 0x1p-228Q;
w.value *= 0x1p-2Q;
return v.value + w.value;
}
v.ieee.mantissa3 |= j;
return v.value * 0x1p-228Q;
}
}