[llvm] [APFloat] add power (PR #122889)

[Matt Arsenault via llvm-commits]

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@@ -1536,6 +1536,26 @@ inline APFloat abs(APFloat X) {
   return X;
 }
 
+/// Returns X^N for N >= 0.
+inline APFloat pow(const APFloat &X, int64_t N) {
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arsenm wrote:

I don't think we should add this unless it's correctly rounded 

https://github.com/llvm/llvm-project/pull/122889