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authorPeter Maydell <peter.maydell@linaro.org>2014-01-07 17:19:12 +0000
committerPeter Maydell <peter.maydell@linaro.org>2014-01-08 19:07:22 +0000
commitf9288a76f1819c2dbf8d2873aebab6aec0f461f5 (patch)
tree2dd23209dc6a2cf78d917e3ca6ecfebee548c6a8 /fpu
parentdc355b764de890e1b5872d0b402dccfd9a9b5286 (diff)
downloadqemu-arm-f9288a76f1819c2dbf8d2873aebab6aec0f461f5.tar.gz
softfloat: Add support for ties-away rounding
IEEE754-2008 specifies a new rounding mode: "roundTiesToAway: the floating-point number nearest to the infinitely precise result shall be delivered; if the two nearest floating-point numbers bracketing an unrepresentable infinitely precise result are equally near, the one with larger magnitude shall be delivered." Implement this new mode (it is needed for ARM). The general principle is that the required code is exactly like the ties-to-even code, except that we do not need to do the "in case of exact tie clear LSB to round-to-even", because the rounding operation naturally causes the exact tie to round up in magnitude. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <rth@twiddle.net>
Diffstat (limited to 'fpu')
-rw-r--r--fpu/softfloat.c54
1 files changed, 54 insertions, 0 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 6c7a90a054..e0ea599769 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -111,6 +111,7 @@ static int32 roundAndPackInt32( flag zSign, uint64_t absZ STATUS_PARAM)
roundNearestEven = ( roundingMode == float_round_nearest_even );
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
roundIncrement = 0x40;
break;
case float_round_to_zero:
@@ -161,6 +162,7 @@ static int64 roundAndPackInt64( flag zSign, uint64_t absZ0, uint64_t absZ1 STATU
roundNearestEven = ( roundingMode == float_round_nearest_even );
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
increment = ((int64_t) absZ1 < 0);
break;
case float_round_to_zero:
@@ -214,6 +216,7 @@ static int64 roundAndPackUint64(flag zSign, uint64_t absZ0,
roundNearestEven = (roundingMode == float_round_nearest_even);
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
increment = ((int64_t)absZ1 < 0);
break;
case float_round_to_zero:
@@ -366,6 +369,7 @@ static float32 roundAndPackFloat32(flag zSign, int_fast16_t zExp, uint32_t zSig
roundNearestEven = ( roundingMode == float_round_nearest_even );
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
roundIncrement = 0x40;
break;
case float_round_to_zero:
@@ -550,6 +554,7 @@ static float64 roundAndPackFloat64(flag zSign, int_fast16_t zExp, uint64_t zSig
roundNearestEven = ( roundingMode == float_round_nearest_even );
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
roundIncrement = 0x200;
break;
case float_round_to_zero:
@@ -734,6 +739,7 @@ static floatx80
zSig0 |= ( zSig1 != 0 );
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
break;
case float_round_to_zero:
roundIncrement = 0;
@@ -794,6 +800,7 @@ static floatx80
precision80:
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
increment = ((int64_t)zSig1 < 0);
break;
case float_round_to_zero:
@@ -838,6 +845,7 @@ static floatx80
if ( zSig1 ) STATUS(float_exception_flags) |= float_flag_inexact;
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
increment = ((int64_t)zSig1 < 0);
break;
case float_round_to_zero:
@@ -1052,6 +1060,7 @@ static float128
roundNearestEven = ( roundingMode == float_round_nearest_even );
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
increment = ((int64_t)zSig2 < 0);
break;
case float_round_to_zero:
@@ -1114,6 +1123,7 @@ static float128
if ( isTiny && zSig2 ) float_raise( float_flag_underflow STATUS_VAR);
switch (roundingMode) {
case float_round_nearest_even:
+ case float_round_ties_away:
increment = ((int64_t)zSig2 < 0);
break;
case float_round_to_zero:
@@ -1785,6 +1795,11 @@ float32 float32_round_to_int( float32 a STATUS_PARAM)
return packFloat32( aSign, 0x7F, 0 );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x7E) {
+ return packFloat32(aSign, 0x7F, 0);
+ }
+ break;
case float_round_down:
return make_float32(aSign ? 0xBF800000 : 0);
case float_round_up:
@@ -1803,6 +1818,9 @@ float32 float32_round_to_int( float32 a STATUS_PARAM)
z &= ~lastBitMask;
}
break;
+ case float_round_ties_away:
+ z += lastBitMask >> 1;
+ break;
case float_round_to_zero:
break;
case float_round_up:
@@ -3183,6 +3201,9 @@ static float32 roundAndPackFloat16(flag zSign, int_fast16_t zExp,
increment = zSig & (increment << 1);
}
break;
+ case float_round_ties_away:
+ increment = (mask + 1) >> 1;
+ break;
case float_round_up:
increment = zSign ? 0 : mask;
break;
@@ -3487,6 +3508,11 @@ float64 float64_round_to_int( float64 a STATUS_PARAM )
return packFloat64( aSign, 0x3FF, 0 );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x3FE) {
+ return packFloat64(aSign, 0x3ff, 0);
+ }
+ break;
case float_round_down:
return make_float64(aSign ? LIT64( 0xBFF0000000000000 ) : 0);
case float_round_up:
@@ -3506,6 +3532,9 @@ float64 float64_round_to_int( float64 a STATUS_PARAM )
z &= ~lastBitMask;
}
break;
+ case float_round_ties_away:
+ z += lastBitMask >> 1;
+ break;
case float_round_to_zero:
break;
case float_round_up:
@@ -4771,6 +4800,11 @@ floatx80 floatx80_round_to_int( floatx80 a STATUS_PARAM )
packFloatx80( aSign, 0x3FFF, LIT64( 0x8000000000000000 ) );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x3FFE) {
+ return packFloatx80(aSign, 0x3FFF, LIT64(0x8000000000000000));
+ }
+ break;
case float_round_down:
return
aSign ?
@@ -4794,6 +4828,9 @@ floatx80 floatx80_round_to_int( floatx80 a STATUS_PARAM )
z.low &= ~lastBitMask;
}
break;
+ case float_round_ties_away:
+ z.low += lastBitMask >> 1;
+ break;
case float_round_to_zero:
break;
case float_round_up:
@@ -5862,6 +5899,15 @@ float128 float128_round_to_int( float128 a STATUS_PARAM )
}
}
break;
+ case float_round_ties_away:
+ if (lastBitMask) {
+ add128(z.high, z.low, 0, lastBitMask >> 1, &z.high, &z.low);
+ } else {
+ if ((int64_t) z.low < 0) {
+ ++z.high;
+ }
+ }
+ break;
case float_round_to_zero:
break;
case float_round_up:
@@ -5893,6 +5939,11 @@ float128 float128_round_to_int( float128 a STATUS_PARAM )
return packFloat128( aSign, 0x3FFF, 0, 0 );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x3FFE) {
+ return packFloat128(aSign, 0x3FFF, 0, 0);
+ }
+ break;
case float_round_down:
return
aSign ? packFloat128( 1, 0x3FFF, 0, 0 )
@@ -5916,6 +5967,9 @@ float128 float128_round_to_int( float128 a STATUS_PARAM )
z.high &= ~ lastBitMask;
}
break;
+ case float_round_ties_away:
+ z.high += lastBitMask>>1;
+ break;
case float_round_to_zero:
break;
case float_round_up: