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Re: [PATCH 2/3] Add more tests for trunc.


On Tue, 24 May 2016, Matt Turner wrote:

> Some implementations of truncf(x) add 2**23 to x with the rounding mode
> set to truncate before subtracting 2**23 to produce the truncated
> result. Unfortunately this doesn't work for odd values of x greater than
> 2**23, since the result of the addition is inexact and the parity bit is
> lost by the rounding step. The same problems apply to implementations of
> trunc on other floating-point data types.

I think the same tests should be added for all of ceil, floor, round, 
trunc if not already present.

> +    TEST_f_f (trunc, 0x1p63 + 1, 0x1p63 + 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
>      TEST_f_f (trunc, 0x1p64, 0x1p64, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
>      TEST_f_f (trunc, 0x1p65, 0x1p65, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
>      TEST_f_f (trunc, 0x1p105, 0x1p105, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
> +    TEST_f_f (trunc, 0x1p105 + 1, 0x1p105 + 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
>      TEST_f_f (trunc, 0x1p106, 0x1p106, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
>      TEST_f_f (trunc, 0x1p107, 0x1p107, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
>      TEST_f_f (trunc, 0x1p112, 0x1p112, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
> +    TEST_f_f (trunc, 0x1p112 + 1, 0x1p112 + 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),

These need to suffix the constants with 'L' so that they actually test 
what's intended for long double.  And doing arithmetic like that in 
libm-test.inc makes manipulation to change suffixes, as in 
<https://sourceware.org/ml/libc-alpha/2016-05/msg00474.html>, harder.  So 
I think it's better to write all the constants explicitly without 
arithmetic (0x1.000002p23L, 0x1.0000000000001p52L, 
0x1.0000000000000002p63L, 0x1.000000000000000000000000008p105L, 
0x1.0000000000000000000000000001p112L).

-- 
Joseph S. Myers
joseph@codesourcery.com


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