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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 <joseph@codesourcery.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>
This commit is contained in:
Joseph Myers 2013-11-04 16:54:15 +00:00 committed by Scott Wood
parent 4f6db5efff
commit d06b3326df
1 changed files with 5 additions and 0 deletions
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5
include/math-emu/op-common.h
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@ -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); \
} \