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msvcrt: Convert double (numerically) to UINT64 via INT64, fixing pow() on arm. 

If converting a negative double to an UINT64, on arm it's clipped
to zero instead of converted to its two's complement form (contrary
to x86).

This fixes cases like pow(2.0, -2.0) on arm/aarch64. Add similar
casts to expf() too which seems to have a similar pattern, even if
it's not known if that case can cause issues or not.

In the original musl source, the converttoint() function returns a
signed int32_t, doing the same double->signed->unsigned conversion,
implicitly.

Signed-off-by: Martin Storsjo <martin@martin.st>
Signed-off-by: Piotr Caban <piotr@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>
This commit is contained in:
Martin Storsjo 2021-07-27 01:28:01 +03:00 committed by Alexandre Julliard
parent 057ecd41cc
commit 37b896db48
1 changed files with 3 additions and 3 deletions
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6
dlls/msvcrt/math.c
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@ -1204,7 +1204,7 @@ float CDECL expf( float x )
ideally ties-to-even rule is used, otherwise the magnitude of r
can be bigger which gives larger approximation error. */
kd = __round(z);
ki = kd;
ki = (INT64)kd;
r = z - kd;
/* exp(x) = 2^(k/N) * 2^(r/N) ~= s * (C0*r^3 + C1*r^2 + C2*r + 1) */
@ -1508,7 +1508,7 @@ static float powf_exp2(double xd, UINT32 sign_bias)
/* N*x = k + r with r in [-1/2, 1/2] */
kd = __round(xd); /* k */
ki = kd;
ki = (INT64)kd;
r = xd - kd;
/* exp2(x) = 2^(k/N) * 2^r ~= s * (C0*r^3 + C1*r^2 + C2*r + 1) */
@ -3824,7 +3824,7 @@ static double pow_exp(double argx, double argy, double x, double xtail, UINT32 s
/* x = ln2/N*k + r, with int k and r in [-ln2/2N, ln2/2N]. */
z = invln2N * x;
kd = __round(z);
ki = kd;
ki = (INT64)kd;
r = x + kd * negln2hiN + kd * negln2loN;
/* The code assumes 2^-200 < |xtail| < 2^-8/N. */
r += xtail;