[libc-commits] [PATCH] D158551: [libc][math] Implement double precision exp function correctly rounded for all rounding modes.

[Tue Ly via Phabricator via libc-commits]

lntue created this revision.
lntue added reviewers: michaelrj, sivachandra, cqlauter, zimmermann6.
Herald added subscribers: luke, sunshaoce, frasercrmck, luismarques, apazos, sameer.abuasal, s.egerton, Jim, jocewei, PkmX, arphaman, the_o, brucehoult, MartinMosbeck, rogfer01, edward-jones, zzheng, jrtc27, niosHD, sabuasal, simoncook, johnrusso, rbar, asb.
Herald added projects: libc-project, All.
lntue requested review of this revision.
Herald added a subscriber: wangpc.

Implement double precision exp function correctly rounded for all
rounding modes.  Using 4 stages:

- Range reduction: reduce to `exp(x) = 2^hi * 2^mid1 * 2^mid2 * exp(lo)`.
- Use 64 + 64 LUT for 2^mid1 and 2^mid2, and use cubic Taylor polynomial to

approximate `(exp(lo) - 1) / lo` in double precision.  Relative error in this
step is bounded by 1.5 * 2^-63.

- If the rounding test fails, use degree-6 Taylor polynomial to approximate

`exp(lo)` in double-double precision.  Relative error in this step is bounded by
2^-99.

- If the rounding test still fails, use degree-7 Taylor polynomial to compute

`exp(lo)` in ~128-bit precision.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D158551

Files:
  libc/config/darwin/arm/entrypoints.txt
  libc/config/linux/aarch64/entrypoints.txt
  libc/config/linux/riscv64/entrypoints.txt
  libc/config/linux/x86_64/entrypoints.txt
  libc/config/windows/entrypoints.txt
  libc/docs/math/index.rst
  libc/spec/stdc.td
  libc/src/__support/CPP/type_traits.h
  libc/src/__support/FPUtil/FMA.h
  libc/src/__support/FPUtil/PolyEval.h
  libc/src/__support/FPUtil/double_double.h
  libc/src/__support/FPUtil/dyadic_float.h
  libc/src/__support/FPUtil/multiply_add.h
  libc/src/math/CMakeLists.txt
  libc/src/math/exp.h
  libc/src/math/generic/CMakeLists.txt
  libc/src/math/generic/exp.cpp
  libc/test/src/math/CMakeLists.txt
  libc/test/src/math/exp_test.cpp
  libc/test/src/math/log10_test.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D158551.552501.patch
Type: text/x-patch
Size: 48998 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/libc-commits/attachments/20230822/fbea672e/attachment-0001.bin>