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Fix f64_to_bf16 raising underflow when it shouldn't #1826

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Oct 1, 2024
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Fix f64_to_bf16 raising underflow when it shouldn't #1826

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46 changes: 39 additions & 7 deletions softfloat/f64_to_bf16.c
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Original file line number Diff line number Diff line change
Expand Up @@ -43,12 +43,44 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

bfloat16_t f64_to_bf16( float64_t a )
{
uint_fast8_t roundingMode = softfloat_roundingMode;
softfloat_roundingMode = softfloat_round_odd;
union ui64_f64 uA;
uint_fast64_t uiA;
bool sign;
int_fast16_t exp;
uint_fast64_t frac;
struct commonNaN commonNaN;
uint_fast16_t uiZ, frac16;
union ui16_f16 uZ;

float32_t f32A = f64_to_f32( a );

softfloat_roundingMode = roundingMode;

return f32_to_bf16( f32A );
/*------------------------------------------------------------------------
*------------------------------------------------------------------------*/
uA.f = a;
uiA = uA.ui;
sign = signF64UI( uiA );
exp = expF64UI( uiA );
frac = fracF64UI( uiA );
/*------------------------------------------------------------------------
*------------------------------------------------------------------------*/
if ( exp == 0x7FF ) {
if ( frac ) {
softfloat_f64UIToCommonNaN( uiA, &commonNaN );
uiZ = softfloat_commonNaNToBF16UI( &commonNaN );
} else {
uiZ = packToBF16UI( sign, 0xFF, 0 );
}
goto uiZ;
}
/*------------------------------------------------------------------------
*------------------------------------------------------------------------*/
frac16 = softfloat_shortShiftRightJam64( frac, 38 );
if ( ! (exp | frac16) ) {
uiZ = packToBF16UI( sign, 0, 0 );
goto uiZ;
}
/*------------------------------------------------------------------------
*------------------------------------------------------------------------*/
return softfloat_roundPackToBF16( sign, exp - 0x381, frac16 | 0x4000 );
uiZ:
uZ.ui = uiZ;
return uZ.f;
}
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