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authorriastradh <riastradh@NetBSD.org>2019-08-01 02:06:31 +0000
committerriastradh <riastradh@NetBSD.org>2019-08-01 02:06:31 +0000
commit593878c5c55d8e45167c34adf5597297a4e8ee01 (patch)
tree2fd70780d520b734b6507b4c25c4dfb5f62c6af0 /sys/dev/microcode/wi
parentf6e6bcf116cb88ae114a73a4bf89dfcdc79e1e38 (diff)
Honour the floating-point rounding mode in floating-point formatting.
C99, Sec. 7.19.6.1 `The fprintf function', paragraph 13, p. 281: (Recommended practice) For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most DECIMAL_DIG, then the result should be correctly rounded. If the number of significant decimal digits is more than DECIMAL_DIG but the source value is exactly representable with DECIMAL_DIG digits, then the result should be an exact representation with trailing zeros. Otherwise, the source value is bounded by two adjacent decimal strings L < U, both having DECIMAL_DIG significant idgits; the value of the resultant decimal string D should satisfy L <= D <= U, _with the extra stipulation that the error should have a correct sign for the current rounding direction_. [emphasis added] The gdtoa code base already supports respecting the floating-point rounding mode, as long as we compile it with Honor_FLT_ROUNDS defined. However, for this to work, fegetround must be available in libc, which it is not currently -- the fenv logic is in libm. Fortunately, we don't have to move all of fenv from libm to libc -- programs that do not link against libm don't have fesetround, so the rounding mode is always the default (barring asm shenanigans that bypass the API -- tough). So use a weak reference to fegetround; by default, assume FE_TONEAREST if it is not defined.
Diffstat (limited to 'sys/dev/microcode/wi')
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