Conversions between the SLEEF and long-double backends currently use double as an intermediate in quad_to_quad_strided_loop.
Examples from casts.cpp:
Sleef_cast_from_doubleq1(static_cast<double>(ld));
static_cast<long double>(cast_sleef_to_double(sleef));
This discards valid precision beyond binary64 in both directions. In particular, x87 long double has a 64-bit significand, while binary64 has only 53 bits.
A value such as 1 + 2**-60 is exactly representable by x87 long double and binary128, but is rounded to 1.0 by the current long-double -> SLEEF cast.
The casts should convert directly between the source and destination formats, preserving signed zero, finite values, subnormals, infinities, and signed NaNs. SLEEF -> long double may be narrowing, but it should round directly to the target format rather than first narrowing to double.
Acceptance criteria:
Long-double -> SLEEF preserves every long-double value exactly.SLEEF -> long double is correctly rounded for the platform format.- No conversion passes through binary64.
- Boundary, subnormal, signed-zero, infinity, NaN, and precision-sensitive round-trip tests are included.
Conversions between the SLEEF and long-double backends currently use
doubleas an intermediate inquad_to_quad_strided_loop.Examples from
casts.cpp:This discards valid precision beyond binary64 in both directions. In particular, x87 long double has a 64-bit significand, while binary64 has only 53 bits.
A value such as
1 + 2**-60is exactly representable by x87 long double and binary128, but is rounded to 1.0 by the currentlong-double -> SLEEFcast.The casts should convert directly between the source and destination formats, preserving signed zero, finite values, subnormals, infinities, and signed NaNs.
SLEEF -> long doublemay be narrowing, but it should round directly to the target format rather than first narrowing to double.Acceptance criteria:
Long-double -> SLEEFpreserves every long-double value exactly.SLEEF -> long doubleis correctly rounded for the platform format.