> Date: Tue, 19 Jan 2021 22:16:32 +0000
> From: Taylor R Campbell <riastr...@netbsd.org>
>
> input: 72057594037927937 -> scanf: 72057594037927937.000000
> frac: 0.500000 0x8.00000000000008p-4 sexp: 57
> uexp: b9
> ufrac: 0080000000000000
> 56 : 00ffffffffffffff
> Unexpected result: 5c80 0000 0000 0000
> expected : 5c80 0000 0000 0001
> 056200: sign: 0 uexp: b9 ufrac: 00 0000 0000 0000
>
> Here frac = 0x8.00000000000008p-4 = (1 + 2^56)/2^57, so
> frac*72057594037927936 = frac * 2^56 = 0x8.00000000000008p52 =
> 0x80000000000000.8p52.
^^^
Excuse me -- the exponent at the very end was a typo. It should read:
> Here frac = 0x8.00000000000008p-4 = (1 + 2^56)/2^57, so
> frac*72057594037927936 = frac * 2^56 = 0x8.00000000000008p52 =
> 0x80000000000000.8.
Or, frac * 2^56 = (1 + 2^56)/2 = 1/2 + 2^55.
