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7c84a5042f
In testing for x86_64 on an AMD processor, I observed libm test failures of the form: testing long double (without inline functions) Failure: Test: log2_downward (0x2.b7e151628aed4p+0) Result: is: 1.44269504088896356633e+00 0xb.8aa3b295c17f67600000p-3 should be: 1.44269504088896356622e+00 0xb.8aa3b295c17f67500000p-3 difference: 1.08420217248550443400e-19 0x8.00000000000000000000p-66 ulp : 1.0000 max.ulp : 0.0000 Maximal error of `log2_downward' is : 1 ulp accepted: 0 ulp These issues arise because the maximum ulps when regenerating on one processor are not the same as on another processor, so regeneration on several processors may be needed when updating libm-test-ulps to avoid failures for some users testing glibc - but such regeneration on multiple processors is inconvenient. Causes can be: on x86 and, for x86_64, for long double, variation in results of x87 instructions for transcendental operations between processors; on x86, variation in compiler excess precision between compiler versions and configurations; on any processor where the compiler may contract expressions using fused multiply-add, variation in what contraction occurs. Although it's hard to be sure libm-test-ulps covers all ulps that may be seen in any configuration for the given architecture, in practice it helps simply to add wider test coverage to make it more likely that, when testing on one processor, the ulps seen are the biggest that can be seen for that function on that processor, and hopefully they are also the biggest that can be seen for that function in other configurations for that architecture. Thus, this patch adds some tests of log2 that increase the ulps I see on x86_64 on an Intel processor, so that hopefully future from-scratch regenerations on that processor will produce ulps big enough not to have errors from testing on AMD processors. These tests were found by randomly generating inputs and seeing what produced ulps larger than those currently in libm-test-ulps. Of course such increases also improve the accuracy of the empirical table of known ulps generated from libm-test-ulps files that goes in the manual. Tested for x86_64 and x86 and ulps updated accordingly. * math/auto-libm-test-in: Add more tests of log2. * math/auto-libm-test-out: Regenerated. * sysdeps/i386/fpu/libm-test-ulps: Update. * sysdeps/x86_64/fpu/libm-test-ulps: Likewise. |
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