From d06b3326dfd02f3f036b670d622fe56eb68a5f30 Mon Sep 17 00:00:00 2001
From: Joseph Myers
Date: Mon, 4 Nov 2013 16:54:15 +0000
Subject: [PATCH] math-emu: fix floating-point to integer overflow detection
On overflow, the math-emu macro _FP_TO_INT_ROUND tries to saturate its
result (subject to the value of rsigned specifying the desired
overflow semantics). However, if the rounding step has the effect of
increasing the exponent so as to cause overflow (if the rounded result
is 1 larger than the largest positive value with the given number of
bits, allowing for signedness), the overflow does not get detected,
meaning that for unsigned results 0 is produced instead of the maximum
unsigned integer with the give number of bits, without an exception
being raised for overflow, and that for signed results the minimum
(negative) value is produced instead of the maximum (positive) value,
again without an exception. This patch makes the code check for
rounding increasing the exponent and adjusts the exponent value as
needed for the overflow check.
Signed-off-by: Joseph Myers
Signed-off-by: Scott Wood
---
include/math-emu/op-common.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/include/math-emu/op-common.h b/include/math-emu/op-common.h
index 70fe5e989ace..6bdf8c61d221 100644
--- a/include/math-emu/op-common.h
+++ b/include/math-emu/op-common.h
@@ -743,12 +743,17 @@ do { \
} \
else \
{ \
+ int _lz0, _lz1; \
if (X##_e <= -_FP_WORKBITS - 1) \
_FP_FRAC_SET_##wc(X, _FP_MINFRAC_##wc); \
else \
_FP_FRAC_SRS_##wc(X, _FP_FRACBITS_##fs - 1 - X##_e, \
_FP_WFRACBITS_##fs); \
+ _FP_FRAC_CLZ_##wc(_lz0, X); \
_FP_ROUND(wc, X); \
+ _FP_FRAC_CLZ_##wc(_lz1, X); \
+ if (_lz1 < _lz0) \
+ X##_e++; /* For overflow detection. */ \
_FP_FRAC_SRL_##wc(X, _FP_WORKBITS); \
_FP_FRAC_ASSEMBLE_##wc(r, X, rsize); \
} \
--
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