softfloat: Fix float64_to_uint64

The comment preceding the float64_to_uint64 routine suggests that
the implementation is broken.  And this is, indeed, the case.

This patch properly implements the conversion of a 64-bit floating
point number to an unsigned, 64 bit integer.

This contribution can be licensed under either the softfloat-2a or -2b
license.

Signed-off-by: Tom Musta <tommusta@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Tom Musta 2014-01-07 17:17:49 +00:00 committed by Peter Maydell
parent 564658dc8c
commit f883b3896e
1 changed files with 93 additions and 8 deletions

View File

@ -203,6 +203,56 @@ static int64 roundAndPackInt64( flag zSign, uint64_t absZ0, uint64_t absZ1 STATU
}
/*----------------------------------------------------------------------------
| Takes the 128-bit fixed-point value formed by concatenating `absZ0' and
| `absZ1', with binary point between bits 63 and 64 (between the input words),
| and returns the properly rounded 64-bit unsigned integer corresponding to the
| input. Ordinarily, the fixed-point input is simply rounded to an integer,
| with the inexact exception raised if the input cannot be represented exactly
| as an integer. However, if the fixed-point input is too large, the invalid
| exception is raised and the largest unsigned integer is returned.
*----------------------------------------------------------------------------*/
static int64 roundAndPackUint64(flag zSign, uint64_t absZ0,
uint64_t absZ1 STATUS_PARAM)
{
int8 roundingMode;
flag roundNearestEven, increment;
roundingMode = STATUS(float_rounding_mode);
roundNearestEven = (roundingMode == float_round_nearest_even);
increment = ((int64_t)absZ1 < 0);
if (!roundNearestEven) {
if (roundingMode == float_round_to_zero) {
increment = 0;
} else if (absZ1) {
if (zSign) {
increment = (roundingMode == float_round_down) && absZ1;
} else {
increment = (roundingMode == float_round_up) && absZ1;
}
}
}
if (increment) {
++absZ0;
if (absZ0 == 0) {
float_raise(float_flag_invalid STATUS_VAR);
return LIT64(0xFFFFFFFFFFFFFFFF);
}
absZ0 &= ~(((uint64_t)(absZ1<<1) == 0) & roundNearestEven);
}
if (zSign && absZ0) {
float_raise(float_flag_invalid STATUS_VAR);
return 0;
}
if (absZ1) {
STATUS(float_exception_flags) |= float_flag_inexact;
}
return absZ0;
}
/*----------------------------------------------------------------------------
| Returns the fraction bits of the single-precision floating-point value `a'.
*----------------------------------------------------------------------------*/
@ -6643,16 +6693,51 @@ uint_fast16_t float64_to_uint16_round_to_zero(float64 a STATUS_PARAM)
return res;
}
/* FIXME: This looks broken. */
uint64_t float64_to_uint64 (float64 a STATUS_PARAM)
/*----------------------------------------------------------------------------
| Returns the result of converting the double-precision floating-point value
| `a' to the 64-bit unsigned integer format. The conversion is
| performed according to the IEC/IEEE Standard for Binary Floating-Point
| Arithmetic---which means in particular that the conversion is rounded
| according to the current rounding mode. If `a' is a NaN, the largest
| positive integer is returned. If the conversion overflows, the
| largest unsigned integer is returned. If 'a' is negative, the value is
| rounded and zero is returned; negative values that do not round to zero
| will raise the inexact exception.
*----------------------------------------------------------------------------*/
uint64_t float64_to_uint64(float64 a STATUS_PARAM)
{
int64_t v;
flag aSign;
int_fast16_t aExp, shiftCount;
uint64_t aSig, aSigExtra;
a = float64_squash_input_denormal(a STATUS_VAR);
v = float64_val(int64_to_float64(INT64_MIN STATUS_VAR));
v += float64_val(a);
v = float64_to_int64(make_float64(v) STATUS_VAR);
return v - INT64_MIN;
aSig = extractFloat64Frac(a);
aExp = extractFloat64Exp(a);
aSign = extractFloat64Sign(a);
if (aSign && (aExp > 1022)) {
float_raise(float_flag_invalid STATUS_VAR);
if (float64_is_any_nan(a)) {
return LIT64(0xFFFFFFFFFFFFFFFF);
} else {
return 0;
}
}
if (aExp) {
aSig |= LIT64(0x0010000000000000);
}
shiftCount = 0x433 - aExp;
if (shiftCount <= 0) {
if (0x43E < aExp) {
float_raise(float_flag_invalid STATUS_VAR);
return LIT64(0xFFFFFFFFFFFFFFFF);
}
aSigExtra = 0;
aSig <<= -shiftCount;
} else {
shift64ExtraRightJamming(aSig, 0, shiftCount, &aSig, &aSigExtra);
}
return roundAndPackUint64(aSign, aSig, aSigExtra STATUS_VAR);
}
uint64_t float64_to_uint64_round_to_zero (float64 a STATUS_PARAM)