Date: Fri, 21 Apr 2017 17:37:49 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH] fix scalbn when result is in the subnormal range On Mon, Apr 03, 2017 at 02:38:13AM +0200, Szabolcs Nagy wrote: > in nearest rounding mode scalbn could introduce double rounding error > when an intermediate value and the final result were both in the > subnormal range e.g. > > scalbn(0x1.7ffffffffffffp-1, -1073) > > returned 0x1p-1073 instead of 0x1p-1074, because the intermediate > computation got rounded to 0x1.8p-1023. > > with the fix an intermediate value can only be in the subnormal range > if the final result is 0 which is correct even after double rounding. > (there still can be two roundings so signals may be raised twice, but > that's only observable with trapping exceptions which is not supported.) OK, applying. Rich
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