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Fix remquo spurious overflows (bug 17978) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Mon, 16 Feb 2015 22:39:11 +0000
- Subject: Fix remquo spurious overflows (bug 17978) [committed]
- Authentication-results: sourceware.org; auth=none
Various remquo implementations, when computing the last three bits of
the quotient, have spurious overflows when 4 times the second argument
to remquo overflows. These overflows can in turn cause bad results in
rounding modes where that overflow results in a finite value. This
patch adds tests to avoid the problem multiplications in cases where
they would overflow, similar to those that control an earlier
multiplication by 8.
Tested for x86_64, x86, mips64 and powerpc. Committed.
2015-02-16 Joseph Myers <joseph@codesourcery.com>
[BZ #17978]
* sysdeps/ieee754/dbl-64/s_remquo.c (__remquo): Do not form
products 4 * y and 2 * y where those would overflow.
* sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c (__remquo):
Likewise.
* sysdeps/ieee754/flt-32/s_remquof.c (__remquof): Likewise.
* sysdeps/ieee754/ldbl-128/s_remquol.c (__remquol): Likewise.
* sysdeps/ieee754/ldbl-128ibm/s_remquol.c (__remquol): Likewise.
* sysdeps/ieee754/ldbl-96/s_remquol.c (__remquol): Likewise.
* math/libm-test.inc (remquo_test_data): Add more tests.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 2f3902a..1cf80e3 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -8764,6 +8764,60 @@ static const struct test_ffI_f1_data remquo_test_data[] =
TEST_ffI_f1 (remquo, -3419, 360, -179, -1, NO_INEXACT_EXCEPTION),
TEST_ffI_f1 (remquo, 3419, -360, 179, -1, NO_INEXACT_EXCEPTION),
TEST_ffI_f1 (remquo, -3419, -360, -179, 1, NO_INEXACT_EXCEPTION),
+
+ TEST_ffI_f1 (remquo, max_value, max_value, plus_zero, 1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, max_value, -max_value, plus_zero, -1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, max_value, min_value, plus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, max_value, -min_value, plus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, max_value, min_subnorm_value, plus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, max_value, -min_subnorm_value, plus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -max_value, max_value, minus_zero, -1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -max_value, -max_value, minus_zero, 1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -max_value, min_value, minus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -max_value, -min_value, minus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -max_value, min_subnorm_value, minus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -max_value, -min_subnorm_value, minus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_value, max_value, min_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_value, -max_value, min_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_value, min_value, plus_zero, 1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_value, -min_value, plus_zero, -1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_value, min_subnorm_value, plus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_value, -min_subnorm_value, plus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_value, max_value, -min_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_value, -max_value, -min_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_value, min_value, minus_zero, -1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_value, -min_value, minus_zero, 1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_value, min_subnorm_value, minus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_value, -min_subnorm_value, minus_zero, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_subnorm_value, max_value, min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_subnorm_value, -max_value, min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_subnorm_value, min_value, min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_subnorm_value, -min_value, min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_subnorm_value, min_subnorm_value, plus_zero, 1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, min_subnorm_value, -min_subnorm_value, plus_zero, -1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_subnorm_value, max_value, -min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_subnorm_value, -max_value, -min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_subnorm_value, min_value, -min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_subnorm_value, -min_value, -min_subnorm_value, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_subnorm_value, min_subnorm_value, minus_zero, -1, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -min_subnorm_value, -min_subnorm_value, minus_zero, 1, NO_INEXACT_EXCEPTION),
+
+ TEST_ffI_f1 (remquo, 1, max_value, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, 1, -max_value, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, 1, max_value / 2, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, 1, -max_value / 2, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, 1, max_value / 4, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, 1, -max_value / 4, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, 1, max_value / 8, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, 1, -max_value / 8, 1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, max_value, -1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, -max_value, -1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, max_value / 2, -1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, -max_value / 2, -1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, max_value / 4, -1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, -max_value / 4, -1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, max_value / 8, -1, 0, NO_INEXACT_EXCEPTION),
+ TEST_ffI_f1 (remquo, -1, -max_value / 8, -1, 0, NO_INEXACT_EXCEPTION),
};
static void
diff --git a/sysdeps/ieee754/dbl-64/s_remquo.c b/sysdeps/ieee754/dbl-64/s_remquo.c
index 2724902..e07efa8 100644
--- a/sysdeps/ieee754/dbl-64/s_remquo.c
+++ b/sysdeps/ieee754/dbl-64/s_remquo.c
@@ -60,12 +60,12 @@ __remquo (double x, double y, int *quo)
y = fabs (y);
cquo = 0;
- if (x >= 4 * y)
+ if (hy <= 0x7fcfffff && x >= 4 * y)
{
x -= 4 * y;
cquo += 4;
}
- if (x >= 2 * y)
+ if (hy <= 0x7fdfffff && x >= 2 * y)
{
x -= 2 * y;
cquo += 2;
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c
index 5b71425..ab56178 100644
--- a/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c
+++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c
@@ -59,12 +59,12 @@ __remquo (double x, double y, int *quo)
INSERT_WORDS64 (y, hy);
cquo = 0;
- if (x >= 4 * y)
+ if (hy <= UINT64_C(0x7fcfffffffffffff) && x >= 4 * y)
{
x -= 4 * y;
cquo += 4;
}
- if (x >= 2 * y)
+ if (hy <= UINT64_C(0x7fdfffffffffffff) && x >= 2 * y)
{
x -= 2 * y;
cquo += 2;
diff --git a/sysdeps/ieee754/flt-32/s_remquof.c b/sysdeps/ieee754/flt-32/s_remquof.c
index a9cdf8f..04944fd 100644
--- a/sysdeps/ieee754/flt-32/s_remquof.c
+++ b/sysdeps/ieee754/flt-32/s_remquof.c
@@ -59,12 +59,12 @@ __remquof (float x, float y, int *quo)
y = fabsf (y);
cquo = 0;
- if (x >= 4 * y)
+ if (hy <= 0x7e7fffff && x >= 4 * y)
{
x -= 4 * y;
cquo += 4;
}
- if (x >= 2 * y)
+ if (hy <= 0x7effffff && x >= 2 * y)
{
x -= 2 * y;
cquo += 2;
diff --git a/sysdeps/ieee754/ldbl-128/s_remquol.c b/sysdeps/ieee754/ldbl-128/s_remquol.c
index 8543265..da175a1 100644
--- a/sysdeps/ieee754/ldbl-128/s_remquol.c
+++ b/sysdeps/ieee754/ldbl-128/s_remquol.c
@@ -61,12 +61,12 @@ __remquol (long double x, long double y, int *quo)
y = fabsl (y);
cquo = 0;
- if (x >= 4 * y)
+ if (hy <= 0x7ffcffffffffffffLL && x >= 4 * y)
{
x -= 4 * y;
cquo += 4;
}
- if (x >= 2 * y)
+ if (hy <= 0x7ffdffffffffffffLL && x >= 2 * y)
{
x -= 2 * y;
cquo += 2;
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_remquol.c b/sysdeps/ieee754/ldbl-128ibm/s_remquol.c
index e36af52..ac22879 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_remquol.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_remquol.c
@@ -66,12 +66,12 @@ __remquol (long double x, long double y, int *quo)
y = fabsl (y);
cquo = 0;
- if (x >= 4 * y)
+ if (hy <= 0x7fcfffffffffffffLL && x >= 4 * y)
{
x -= 4 * y;
cquo += 4;
}
- if (x >= 2 * y)
+ if (hy <= 0x7fdfffffffffffffLL && x >= 2 * y)
{
x -= 2 * y;
cquo += 2;
diff --git a/sysdeps/ieee754/ldbl-96/s_remquol.c b/sysdeps/ieee754/ldbl-96/s_remquol.c
index 6b3499d..1462b54 100644
--- a/sysdeps/ieee754/ldbl-96/s_remquol.c
+++ b/sysdeps/ieee754/ldbl-96/s_remquol.c
@@ -60,12 +60,12 @@ __remquol (long double x, long double p, int *quo)
p = fabsl (p);
cquo = 0;
- if (x >= 4 * p)
+ if (ep <= 0x7ffc && x >= 4 * p)
{
x -= 4 * p;
cquo += 4;
}
- if (x >= 2 * p)
+ if (ep <= 0x7ffd && x >= 2 * p)
{
x -= 2 * p;
cquo += 2;
--
Joseph S. Myers
joseph@codesourcery.com