Incorrect return values for pow(-1,nan) and tgamma(-inf) (IDFGH-5559)

[dpgeorge]

Environment

• Module or chip used: ESP32-PICO-D4 and ESP32C3
• IDF version: v4.4-dev-2128-gf45b60b28
• Build System: idf.py
• Compiler version: xtensa-esp32-elf-gcc (crosstool-NG esp-2021r1) 8.4.0
• Operating System: Linux

Problem Description

The return value of pow(-1, NAN) and tgamma(-INFINITY) are incorrect (according to standard C function semantics).

Expected Behavior

• pow(-1, NAN) should return NAN; see https://pubs.opengroup.org/onlinepubs/9699919799/functions/pow.html
• tgamma(-INFINITY) should return NAN; see https://pubs.opengroup.org/onlinepubs/9699919799/functions/tgamma.html

Actual Behavior

• pow(-1, NAN) returns -1.000
• tgamma(-INFINITY) returns INFINITY

Steps to reproduce / code

Create a simple program (eg based on hello_world) and add these lines:

    printf("pow(-1, nan) = %f\n", pow(-1, NAN));
    printf("tgamma(-inf) = %f\n", tgamma(-INFINITY));

Then compile, flash, run, and inspect output.

[0xjakob]

@dpgeorge I think I found the issue with the pow() function. It seems to be a toolchain bug in newlib which has been fixed in newer versions than the one IDF uses. I'll check tgamma() as well. We'll probably provide a quick fix for IDF versions and/or include the fix in the newer IDF toolchain releases.

[0xjakob]

It's been fixed, but only very recently: https://sourceware.org/git/?p=newlib-cygwin.git;a=commit;h=bb25dd1b0f39f343b764fd0db861cb9a30441407

[zikalino]

@dpgeorge we should have a fix for this issue very soon, as we will be upgrading toolchains to 2022r1.