[PATCH 3/6] math-emu: fix floating-point to integer unsigned saturation

From: Joseph S. Myers
Date: Mon Nov 04 2013 - 11:53:58 EST


From: Joseph Myers <joseph@xxxxxxxxxxxxxxxx>

The math-emu macros _FP_TO_INT and _FP_TO_INT_ROUND are supposed to
saturate their results for out-of-range arguments, except in the case
rsigned == 2 (when instead the low bits of the result are taken).
However, in the case rsigned == 0 (converting to unsigned integers),
they mistakenly produce 0 for positive results and the maximum
unsigned integer for negative results, the opposite of correct
unsigned saturation. This patch fixes the logic.

Signed-off-by: Joseph Myers <joseph@xxxxxxxxxxxxxxxx>

---

Previous submission: <http://lkml.org/lkml/2013/10/8/694>.

I have made the corresponding changes to the glibc/libgcc copy of this
code, given that it would be desirable to resync the Linux and
glibc/libgcc copies (the latter has had many enhancements and bug
fixes since it was copied into Linux), although strictly this
incorrect saturation is only a bug when trying to emulate particular
instruction semantics, not when used in userspace to implement C
operations where the results of out-of-range conversions are
unspecified or undefined.

diff --git a/include/math-emu/op-common.h b/include/math-emu/op-common.h
index 9696a5e..70fe5e9 100644
--- a/include/math-emu/op-common.h
+++ b/include/math-emu/op-common.h
@@ -685,7 +685,7 @@ do { \
else \
{ \
r = 0; \
- if (X##_s) \
+ if (!X##_s) \
r = ~r; \
} \
FP_SET_EXCEPTION(FP_EX_INVALID); \
@@ -762,7 +762,7 @@ do { \
if (!rsigned) \
{ \
r = 0; \
- if (X##_s) \
+ if (!X##_s) \
r = ~r; \
} \
else if (rsigned != 2) \

--
Joseph S. Myers
joseph@xxxxxxxxxxxxxxxx
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