[HELP] Why does libm not have nextafter?

[sastel]

Description

I'm working on getting gtest executables to compile for kernel mode, so that I can run my tests on the target hardware. The EXPECT_NEAR tests in gtest rely on nextafter(). So my tests fail to link, because libm doesn't have a definition for nextafter().

Does anyone know why this function was not included in libm? I can add it myself, but I'm wondering if there is a fundamental reason that I need to be aware of for why it isn't already present.

Using libmcs isn't an option for me, because RISC-V RV64 uses 128 bit long double, and libmcs only supports 64 bit long double in order to comply with IEEE-754. I tried newlib, but the cmath header fails to compile due to references to the undeclared long double versions of the math functions, which is the same symptom I get when I compile libmcs without long double.

Verification

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[acassis]

Hi @sastel I think it is not included because nobody used it until now. Also ANSI C doesn't require this function: https://docs.rtems.org/releases/4.5.1-pre3/toolsdoc/newlib-1.8.2-docs/libm/libm00036.html

[sastel]

Thanks @acassis .

[acassis]

@sastel if you submit an implementation, please link to this Issue here for future reference.