include/cxx/{cstdlib,cmath}: Provide std::abs(float) overloads

[mpflanzer]

Summary

The new overloads of std::abs added to cstdlib and cmath are defined as specified by the C++ standard: https://en.cppreference.com/cpp/numeric/math/fabs

Without these new definitions the int std::abs(int) function, provided by using ::abs, was selected for all argument types resulting in a truncation of the result.

Impact

Improved compatibility with the C++ standard

Testing

#include <cstdio>
#include <cstdlib>
#include <float.h>

extern "C" int main(int argc, FAR char *argv[]) {
  printf("FLT_MAX = %f\n", FLT_MAX);
  printf("DBL_MAX = %f\n", DBL_MAX);
  printf("INT_MAX = %d\n", INT_MAX);
  printf("LONG_MAX = %ld\n", LONG_MAX);
  printf("LLONG_MAX = %lld\n", LLONG_MAX);

  printf("::abs(FLT_MAX) = %d\n", ::abs(4.2));
  printf("::abs(DBL_MAX) = %d\n", ::abs(4.2));
  printf("::abs(INT_MAX) = %d\n", ::abs(INT_MAX));
  printf("::abs(LONG_MAX) = %ld\n", ::abs(LONG_MAX));
  printf("::abs(LLONG_MAX) = %lld\n", ::abs(LLONG_MAX));
  printf("std::abs(FLT_MAX) = %f\n", std::abs(FLT_MAX));
  printf("std::abs(DBL_MAX) = %f\n", std::abs(DBL_MAX));
  printf("std::abs(INT_MAX) = %d\n", std::abs(INT_MAX));
  printf("std::abs(LONG_MAX) = %ld\n", std::abs(LONG_MAX));
  printf("std::abs(LLONG_MAX) = %lld\n", std::abs(LLONG_MAX));

  return 0;
}

Without the changes running this program results in the following output:

FLT_MAX = 340282346638529000000000000000000000000.000000
DBL_MAX = 179769313486232000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000
INT_MAX = 2147483647
LONG_MAX = 2147483647
LLONG_MAX = 9223372036854775807
::abs(FLT_MAX) = 4
::abs(DBL_MAX) = 4
::abs(INT_MAX) = 2147483647
::abs(LONG_MAX) = 2147483647
::abs(LLONG_MAX) = 19327352830
std::abs(FLT_MAX) = 0.000000
std::abs(DBL_MAX) = 0.000000
std::abs(INT_MAX) = 2147483647
std::abs(LONG_MAX) = 2147483647
std::abs(LLONG_MAX) = 19327352830

That is compliant for ::abs but not for std::abs.

With the changes the right overloads of std::abs are selected and the output is:

FLT_MAX = 340282346638529000000000000000000000000.000000
DBL_MAX = 179769313486232000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000
INT_MAX = 2147483647
LONG_MAX = 2147483647
LLONG_MAX = 9223372036854775807
::abs(FLT_MAX) = 4
::abs(DBL_MAX) = 4
::abs(INT_MAX) = 2147483647
::abs(LONG_MAX) = 2147483647
::abs(LLONG_MAX) = 19327352830
std::abs(FLT_MAX) = 340282346638529000000000000000000000000.000000
std::abs(DBL_MAX) = 179769313486232000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000
std::abs(INT_MAX) = 2147483647
std::abs(LONG_MAX) = 2147483647
std::abs(LLONG_MAX) = 9223372036854775807

Tested with the qemu-armv7a:nsh config

[mpflanzer]

How shall I address the style errors in the std_abs.h file? It currently follows the same style as the other files in the cxx directory. Those seem pass unchecked because they don't have a .h extension.

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb

[xiaoxiang781216]

@mpflanzer please fix ci error: https://github.com/apache/nuttx/actions/runs/32227114781/job/96215519806?pr=19891