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softfloat: Fix single-to-half precision float conversions

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Fix various bugs in the single-to-half-precision conversion code:
 * input NaNs not correctly converted in IEEE mode
   (fixed by defining and using a commonNaNToFloat16())
 * wrong values returned when converting NaN/Inf into non-IEEE
   half precision value
 * wrong values returned for conversion of values which are
   on the boundary between denormal and zero for the half
   precision format
 * zeroes not correctly identified
 * excessively large results in non-IEEE mode should
   generate InvalidOp, not Overflow

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Peter Maydell 2011-02-10 11:28:58 +00:00 • committed by Aurelien Jarno
parent bcd4d9afd4
commit 600e30d2b2
2 changed files with 38 additions and 11 deletions
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21
fpu/softfloat-specialize.h
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@ -119,6 +119,27 @@ float16 float16_maybe_silence_nan(float16 a_)
return a_;
}
/*----------------------------------------------------------------------------
| Returns the result of converting the canonical NaN `a' to the half-
| precision floating-point format.
*----------------------------------------------------------------------------*/
static float16 commonNaNToFloat16(commonNaNT a STATUS_PARAM)
{
uint16_t mantissa = a.high>>54;
if (STATUS(default_nan_mode)) {
return float16_default_nan;
}
if (mantissa) {
return make_float16(((((uint16_t) a.sign) << 15)
| (0x1F << 10) | mantissa));
} else {
return float16_default_nan;
}
}
/*----------------------------------------------------------------------------
| The pattern for a default generated single-precision NaN.
*----------------------------------------------------------------------------*/