softfloat: Fix factor 2 error for scalbn on denormal inputs
If the input to float*_scalbn() is denormal then it represents a number 0.[mantissabits] * 2^(1-exponentbias) (and the actual exponent field is all zeroes). This means that when we convert it to our unpacked encoding the unpacked exponent must be one greater than for a normal number, which represents 1.[mantissabits] * 2^(e-exponentbias) for an exponent field e. This meant we were giving answers too small by a factor of 2 for all denormal inputs. Note that the float-to-int routines also have this behaviour of not adjusting the exponent for denormals; however there it is harmless because denormals will all convert to integer zero anyway. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Aurelien Jarno <aurelien@aurel32.net> Reviewed-by: Richard Henderson <rth@twiddle.net>
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@ -6991,10 +6991,13 @@ float32 float32_scalbn( float32 a, int n STATUS_PARAM )
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}
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return a;
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}
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if ( aExp != 0 )
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if (aExp != 0) {
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aSig |= 0x00800000;
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else if ( aSig == 0 )
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} else if (aSig == 0) {
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return a;
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} else {
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aExp++;
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}
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if (n > 0x200) {
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n = 0x200;
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@ -7024,10 +7027,13 @@ float64 float64_scalbn( float64 a, int n STATUS_PARAM )
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}
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return a;
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}
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if ( aExp != 0 )
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if (aExp != 0) {
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aSig |= LIT64( 0x0010000000000000 );
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else if ( aSig == 0 )
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} else if (aSig == 0) {
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return a;
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} else {
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aExp++;
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}
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if (n > 0x1000) {
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n = 0x1000;
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@ -7057,8 +7063,12 @@ floatx80 floatx80_scalbn( floatx80 a, int n STATUS_PARAM )
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return a;
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}
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if (aExp == 0 && aSig == 0)
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return a;
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if (aExp == 0) {
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if (aSig == 0) {
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return a;
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}
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aExp++;
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}
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if (n > 0x10000) {
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n = 0x10000;
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@ -7087,10 +7097,13 @@ float128 float128_scalbn( float128 a, int n STATUS_PARAM )
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}
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return a;
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}
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if ( aExp != 0 )
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if (aExp != 0) {
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aSig0 |= LIT64( 0x0001000000000000 );
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else if ( aSig0 == 0 && aSig1 == 0 )
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} else if (aSig0 == 0 && aSig1 == 0) {
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return a;
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} else {
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aExp++;
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}
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if (n > 0x10000) {
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n = 0x10000;
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