[PATCH] PowerPC - Fix PPC64 floorl
Adhemerval Zanella
azanella@linux.vnet.ibm.com
Fri Apr 20 20:54:00 GMT 2012
On 04/19/2012 06:26 PM, Joseph S. Myers wrote:
> On Thu, 19 Apr 2012, Steven Munroe wrote:
>
>>> I don't see how that can be correct. If the high part is small, but an
>>> integer, the result of this function should still depend on whether the
>>> low part is positive, negative or zero. Presumably the testsuite failed
>>> to detect that bug in this patch, meaning you also need tests (conditioned
>>> on TEST_LDOUBLE - they can be written to be valid for all long double
>>> formats) for values that when rounded to 53 bits are an integer, but
>>> differ from the integer value in lower bits (covering at least the four
>>> cases of positive and negative value, above and below the exact integer it
>>> is close to).
>> Are you concerned that xh may be "prerounded" away (from default
>> rounding mode)? This is not what we want for floor. In which case we
>> should "deround" xh before the __floor operation.
>> Perhaps:
>>
>> + if (__builtin_expect(__builtin_fabs (x) < two52, 1))
>> + return ldbl_pack (__floor (xh+xl), -0.0);
> That won't help either.
>
> In a valid long double, xh is always the value of the long double, rounded
> to nearest, independent of the current rounding direction; that's the
> definition of the format. The result of floorl doesn't depend on the
> current rounding direction either; it always rounds to an integer value in
> the direction of negative infinity.
>
> If xh is an integer, and xl is positive or zero with absolute value less
> than 1, xh is the correct result of floorl. If xh is an integer, and xl
> is negative with absolute value less than 1, the correct result of floorl
> is xh - 1. (If xl has absolute value at least 1, which means xh is large,
> then the correct result is xh + floor(xl); that formula is indeed correct
> whenever xh is an integer. And if xh is not an integer, the correct
> result is floor (xh).)
>
> The sort of case where I expect this patch will get things wrong is floorl
> (0x1p51L - 0x1p-10L) or floorl (-0x1p51L - 0x1p-10L).
>
Indeed the cases you noted failed with both the old assembly and optimization
I added based on the assembly. This patch now just use the C version and
remove the wrong assembly version.
--
[PATCH] PowerPC - Fix PPC64 floorl
The assembly version fails to correctly floorl some edge cases. The patch
removes it and use the C version.
2012-04-17 Adhemerval Zanella <azanella@linux.vnet.ibm.com>
[BZ #3866]
* sysdeps/powerpc/powerpc64/fpu/s_floorl.S: Delete file. Using the
sysdeps/ieee754/ldbl-128ibm/s_floorl.c version.
* math/libm-test.inc: (floor_test): Add more tests.
* sysdeps/powerpc/fpu/libm-test-ulps: Update for pow tests.
--
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 94d60bf..e91aa26 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -3442,6 +3442,9 @@ floor_test (void)
TEST_f_f (floor, 10141204801825835211973625643008.5L, 10141204801825835211973625643008.0L);
TEST_f_f (floor, 10141204801825835211973625643008.75L, 10141204801825835211973625643008.0L);
TEST_f_f (floor, 10141204801825835211973625643009.5L, 10141204801825835211973625643009.0L);
+
+ TEST_f_f (floor, 0xf.ffffffffffffff8p+47L, 0xf.fffffffffffep+47L);
+ TEST_f_f (floor, -0x8.000000000000004p+48L, -0x8.000000000001p+48L);
#endif
END (floor);
diff --git a/sysdeps/powerpc/fpu/libm-test-ulps b/sysdeps/powerpc/fpu/libm-test-ulps
index 1ab3d4a..c555297 100644
--- a/sysdeps/powerpc/fpu/libm-test-ulps
+++ b/sysdeps/powerpc/fpu/libm-test-ulps
@@ -1488,6 +1488,17 @@ Test "log2 (e) == M_LOG2El":
ildouble: 1
ldouble: 1
+# pow
+Test "pow (0x0.ffffffp0, -0x1p24) == 2.7182819094701610539628664526874952929416":
+float: 1
+ifloat: 1
+Test "pow (0x0.ffffffp0, 0x1p24) == 0.3678794302077803437135155590023422899744":
+float: 1
+ifloat: 1
+Test "pow (0x1.000002p0, 0x1p24) == 7.3890552180866447284268641248075832310141":
+float: 1
+ifloat: 1
+
# pow_downward
Test "pow_downward (1.0625, 1.125) == 1.070582293028761362162622578677070098674":
ildouble: 1
@@ -2448,6 +2459,8 @@ ildouble: 1
ldouble: 1
Function: "pow":
+float: 1
+ifloat: 1
ildouble: 1
ldouble: 1
diff --git a/sysdeps/powerpc/powerpc64/fpu/s_floorl.S b/sysdeps/powerpc/powerpc64/fpu/s_floorl.S
deleted file mode 100644
index 578be43..0000000
--- a/sysdeps/powerpc/powerpc64/fpu/s_floorl.S
+++ /dev/null
@@ -1,133 +0,0 @@
-/* long double floor function.
- IBM extended format long double version.
- Copyright (C) 2004, 2006 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- 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 <sysdep.h>
-#include <math_ldbl_opt.h>
-
- .section ".toc","aw"
-.LC0: /* 2**52 */
- .tc FD_43300000_0[TC],0x4330000000000000
-
- .section ".text"
-/* long double [fp1,fp2] floorl (long double x [fp1,fp2])
- IEEE 1003.1 floor function.
-
- PowerPC64 long double uses the IBM extended format which is
- represented two 64-floating point double values. The values are
- non-overlapping giving an effective precision of 106 bits. The first
- double contains the high order bits of mantisa and is always rounded
- to represent a normal rounding of long double to double. Since the
- long double value is sum of the high and low values, the low double
- normally has the opposite sign to compensate for the this rounding.
-
- For long double there are two cases:
- 1) |x| < 2**52, all the integer bits are in the high double.
- floor the high double and set the low double to -0.0.
- 2) |x| >= 2**52, Rounding involves both doubles.
- See the comment before lable .L2 for details.
- */
-
-ENTRY (__floorl)
- mffs fp11 /* Save current FPU rounding mode. */
- lfd fp13,.LC0@toc(2)
- fabs fp0,fp1
- fabs fp9,fp2
- fsub fp12,fp13,fp13 /* generate 0.0 */
- fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO52) */
- fcmpu cr6,fp1,fp12 /* if (x > 0.0) */
- bnl- cr7,.L2
- mtfsfi 7,3 /* Set rounding mode toward -inf. */
- fneg fp2,fp12 /* set low double to -0.0. */
- ble- cr6,.L0
- fadd fp1,fp1,fp13 /* x+= TWO52; */
- fsub fp1,fp1,fp13 /* x-= TWO52; */
- fcmpu cr5,fp1,fp12 /* if (x > 0.0) */
- mtfsf 0x01,fp11 /* restore previous rounding mode. */
- bnelr+ cr5
- fmr fp1,fp12 /* x must be +0.0 for the 0.0 case. */
- blr
-.L0:
- bge- cr6,.L1 /* if (x < 0.0) */
- fsub fp1,fp1,fp13 /* x-= TWO52; */
- fadd fp1,fp1,fp13 /* x+= TWO52; */
-.L1:
- mtfsf 0x01,fp11 /* restore previous rounding mode. */
- blr
-
-
-/* The high double is > TWO52 so we need to round the low double and
- perhaps the high double. In this case we have to round the low
- double and handle any adjustment to the high double that may be
- caused by rounding (up). This is complicated by the fact that the
- high double may already be rounded and the low double may have the
- opposite sign to compensate.This gets a bit tricky so we use the
- following algorithm:
-
- tau = floor(x_high/TWO52);
- x0 = x_high - tau;
- x1 = x_low + tau;
- r1 = rint(x1);
- y_high = x0 + r1;
- y_low = x0 - y_high + r1;
- return y; */
-.L2:
- fcmpu cr7,fp9,fp13 /* if (|x_low| > TWO52) */
- fcmpu cr0,fp9,fp12 /* || (|x_low| == 0.0) */
- fcmpu cr5,fp2,fp12 /* if (x_low > 0.0) */
- bgelr- cr7 /* return x; */
- beqlr- cr0
- mtfsfi 7,3 /* Set rounding mode toward -inf. */
- fdiv fp8,fp1,fp13 /* x_high/TWO52 */
-
- bng- cr6,.L6 /* if (x > 0.0) */
- fctidz fp0,fp8
- fcfid fp8,fp0 /* tau = floor(x_high/TWO52); */
- bng cr5,.L4 /* if (x_low > 0.0) */
- fmr fp3,fp1
- fmr fp4,fp2
- b .L5
-.L4: /* if (x_low < 0.0) */
- fsub fp3,fp1,fp8 /* x0 = x_high - tau; */
- fadd fp4,fp2,fp8 /* x1 = x_low + tau; */
-.L5:
- fadd fp5,fp4,fp13 /* r1 = r1 + TWO52; */
- fsub fp5,fp5,fp13 /* r1 = r1 - TWO52; */
- b .L9
-.L6: /* if (x < 0.0) */
- fctidz fp0,fp8
- fcfid fp8,fp0 /* tau = floor(x_high/TWO52); */
- bnl cr5,.L7 /* if (x_low < 0.0) */
- fmr fp3,fp1
- fmr fp4,fp2
- b .L8
-.L7: /* if (x_low > 0.0) */
- fsub fp3,fp1,fp8 /* x0 = x_high - tau; */
- fadd fp4,fp2,fp8 /* x1 = x_low + tau; */
-.L8:
- fsub fp5,fp4,fp13 /* r1-= TWO52; */
- fadd fp5,fp5,fp13 /* r1+= TWO52; */
-.L9:
- mtfsf 0x01,fp11 /* restore previous rounding mode. */
- fadd fp1,fp3,fp5 /* y_high = x0 + r1; */
- fsub fp2,fp3,fp1 /* y_low = x0 - y_high + r1; */
- fadd fp2,fp2,fp5
- blr
-END (__floorl)
-
-long_double_symbol (libm, __floorl, floorl)
--
1.6.0.2
--
Adhemerval Zanella Netto
Software Engineer
Linux Technology Center Brazil
Toolchain / GLIBC on Power Architecture
azanella@linux.vnet.ibm.com / azanella@br.ibm.com
+55 61 8642-9890
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