[libc-commits] [PATCH] D122688: [libc][obvious] fix sqrt when long double is double

Michael Jones via Phabricator via libc-commits libc-commits at lists.llvm.org
Tue Mar 29 14:55:47 PDT 2022

michaelrj created this revision.
michaelrj added reviewers: sivachandra, lntue.
Herald added subscribers: libc-commits, ecnelises, tschuett, pengfei.
Herald added projects: libc-project, All.
michaelrj requested review of this revision.

Previously, the "fsqrt" instruction was used on all x86_64 platforms
for finding the square root of long doubles. On long double is double
platforms (e.g. windows) this created errors. This patch changes square
root function for long doubles to be the same as the one for doubles if
long doubles are doubles.

  rG LLVM Github Monorepo



Index: libc/src/__support/FPUtil/x86_64/sqrt.h
--- libc/src/__support/FPUtil/x86_64/sqrt.h
+++ libc/src/__support/FPUtil/x86_64/sqrt.h
@@ -32,10 +32,18 @@
   return result;
+template <> inline long double sqrt<long double>(long double x) {
+  long double result;
+  __asm__ __volatile__("sqrtsd %x1, %x0" : "=x"(result) : "x"(x));
+  return result;
 template <> inline long double sqrt<long double>(long double x) {
   __asm__ __volatile__("fsqrt" : "+t"(x));
   return x;
 } // namespace fputil
 } // namespace __llvm_libc

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