[all-commits] [llvm/llvm-project] bc7a3b: [libc][math] Implement powf function correctly rou...

[lntue via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bc7a3bd864be696217c4d11eddf16bed7646b60f
      https://github.com/llvm/llvm-project/commit/bc7a3bd864be696217c4d11eddf16bed7646b60f
  Author: lntue <35648136+lntue at users.noreply.github.com>
  Date:   2023-11-06 (Mon, 06 Nov 2023)

  Changed paths:
    M libc/config/darwin/arm/entrypoints.txt
    M libc/config/linux/aarch64/entrypoints.txt
    M libc/config/linux/riscv/entrypoints.txt
    M libc/config/linux/x86_64/entrypoints.txt
    M libc/config/windows/entrypoints.txt
    M libc/docs/math/index.rst
    M libc/spec/stdc.td
    M libc/src/math/generic/CMakeLists.txt
    M libc/src/math/generic/common_constants.cpp
    M libc/src/math/generic/common_constants.h
    M libc/src/math/generic/exp10f.cpp
    A libc/src/math/generic/exp10f_impl.h
    M libc/src/math/generic/exp2f.cpp
    A libc/src/math/generic/exp2f_impl.h
    M libc/src/math/generic/log2f.cpp
    A libc/src/math/generic/powf.cpp
    M libc/test/UnitTest/FPMatcher.h
    M libc/test/src/math/CMakeLists.txt
    A libc/test/src/math/powf_test.cpp
    M libc/test/src/math/smoke/CMakeLists.txt
    A libc/test/src/math/smoke/powf_test.cpp
    M libc/utils/MPFRWrapper/MPFRUtils.cpp
    M libc/utils/MPFRWrapper/MPFRUtils.h

  Log Message:
  -----------
  [libc][math] Implement powf function correctly rounded to all rounding modes. (#71188)

We compute `pow(x, y)` using the formula
```
  pow(x, y) = x^y = 2^(y * log2(x))
```
We follow similar steps as in `log2f(x)` and `exp2f(x)`, by breaking
down into `hi + mid + lo` parts, in which `hi` parts are computed using
the exponent field directly, `mid` parts will use look-up tables, and
`lo` parts are approximated by polynomials.

We add some speedup for common use-cases:
```
  pow(2, y) = exp2(y)
  pow(10, y) = exp10(y)
  pow(x, 2) = x * x
  pow(x, 1/2) = sqrt(x)
  pow(x, -1/2) = rsqrt(x) - to be added
```