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soft-fp: Refine FP_EX_DENORM handling for comparisons
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Thu, 5 Feb 2015 21:52:05 +0000
- Subject: soft-fp: Refine FP_EX_DENORM handling for comparisons
- Authentication-results: sourceware.org; auth=none
In <https://sourceware.org/ml/libc-alpha/2014-09/msg00488.html>, I
noted that comparisons in soft-fp did not set FP_EX_DENORM unless
denormal operands were flushed to zero.
This patch fixes soft-fp to check for denormal operands for
comparisons and set that exception whenever FP_EX_DENORM is not zero.
In particular, for the one architecture for which the Linux kernel
defines FP_EX_DENORM (alpha), this corresponds to the existing logic
for comparisons and so allows that logic to be replaced by a simple
call to FP_CMP_D when soft-fp is updated in the kernel.
Tested for powerpc (e500) that installed stripped shared libraries are
unchanged by this patch. Will commit once master reopens for 2.22
development.
2015-02-05 Joseph Myers <joseph@codesourcery.com>
* soft-fp/op-common.h (_FP_CMP_CHECK_DENORM): New macro.
(_FP_CMP_CHECK_FLUSH_ZERO): Likewise.
(_FP_CMP): Use_FP_CMP_CHECK_DENORM and _FP_CMP_CHECK_FLUSH_ZERO.
(_FP_CMP_EQ): Likewise.
(_FP_CMP_UNORD): Use _FP_CMP_CHECK_DENORM.
diff --git a/soft-fp/op-common.h b/soft-fp/op-common.h
index 6b8b52f..a39baa9 100644
--- a/soft-fp/op-common.h
+++ b/soft-fp/op-common.h
@@ -1251,6 +1251,46 @@
} \
while (0)
+/* Helper for comparisons. If denormal operands would raise an
+ exception, check for them, and flush to zero as appropriate
+ (otherwise, we need only check and flush to zero if it might affect
+ the result, which is done later with _FP_CMP_CHECK_FLUSH_ZERO). */
+#define _FP_CMP_CHECK_DENORM(fs, wc, X, Y) \
+ do \
+ { \
+ if (FP_EX_DENORM != 0) \
+ { \
+ /* We must ensure the correct exceptions are raised for \
+ denormal operands, even though this may not affect the \
+ result of the comparison. */ \
+ if (FP_DENORM_ZERO) \
+ { \
+ _FP_CHECK_FLUSH_ZERO (fs, wc, X); \
+ _FP_CHECK_FLUSH_ZERO (fs, wc, Y); \
+ } \
+ else \
+ { \
+ if ((X##_e == 0 && !_FP_FRAC_ZEROP_##wc (X)) \
+ || (Y##_e == 0 && !_FP_FRAC_ZEROP_##wc (Y))) \
+ FP_SET_EXCEPTION (FP_EX_DENORM); \
+ } \
+ } \
+ } \
+ while (0)
+
+/* Helper for comparisons. Check for flushing denormals for zero if
+ we didn't need to check earlier for any denormal operands. */
+#define _FP_CMP_CHECK_FLUSH_ZERO(fs, wc, X, Y) \
+ do \
+ { \
+ if (FP_EX_DENORM == 0) \
+ { \
+ _FP_CHECK_FLUSH_ZERO (fs, wc, X); \
+ _FP_CHECK_FLUSH_ZERO (fs, wc, Y); \
+ } \
+ } \
+ while (0)
+
/* Main differential comparison routine. The inputs should be raw not
cooked. The return is -1, 0, 1 for normal values, UN
otherwise. */
@@ -1258,6 +1298,7 @@
#define _FP_CMP(fs, wc, ret, X, Y, un, ex) \
do \
{ \
+ _FP_CMP_CHECK_DENORM (fs, wc, X, Y); \
/* NANs are unordered. */ \
if ((X##_e == _FP_EXPMAX_##fs && !_FP_FRAC_ZEROP_##wc (X)) \
|| (Y##_e == _FP_EXPMAX_##fs && !_FP_FRAC_ZEROP_##wc (Y))) \
@@ -1270,8 +1311,7 @@
int _FP_CMP_is_zero_x; \
int _FP_CMP_is_zero_y; \
\
- _FP_CHECK_FLUSH_ZERO (fs, wc, X); \
- _FP_CHECK_FLUSH_ZERO (fs, wc, Y); \
+ _FP_CMP_CHECK_FLUSH_ZERO (fs, wc, X, Y); \
\
_FP_CMP_is_zero_x \
= (!X##_e && _FP_FRAC_ZEROP_##wc (X)) ? 1 : 0; \
@@ -1306,6 +1346,7 @@
#define _FP_CMP_EQ(fs, wc, ret, X, Y, ex) \
do \
{ \
+ _FP_CMP_CHECK_DENORM (fs, wc, X, Y); \
/* NANs are unordered. */ \
if ((X##_e == _FP_EXPMAX_##fs && !_FP_FRAC_ZEROP_##wc (X)) \
|| (Y##_e == _FP_EXPMAX_##fs && !_FP_FRAC_ZEROP_##wc (Y))) \
@@ -1315,8 +1356,7 @@
} \
else \
{ \
- _FP_CHECK_FLUSH_ZERO (fs, wc, X); \
- _FP_CHECK_FLUSH_ZERO (fs, wc, Y); \
+ _FP_CMP_CHECK_FLUSH_ZERO (fs, wc, X, Y); \
\
(ret) = !(X##_e == Y##_e \
&& _FP_FRAC_EQ_##wc (X, Y) \
@@ -1331,6 +1371,7 @@
#define _FP_CMP_UNORD(fs, wc, ret, X, Y, ex) \
do \
{ \
+ _FP_CMP_CHECK_DENORM (fs, wc, X, Y); \
(ret) = ((X##_e == _FP_EXPMAX_##fs && !_FP_FRAC_ZEROP_##wc (X)) \
|| (Y##_e == _FP_EXPMAX_##fs && !_FP_FRAC_ZEROP_##wc (Y))); \
if (ret) \
--
Joseph S. Myers
joseph@codesourcery.com