[libclc] [libclc] Move sign to the CLC builtins library (PR #115699)

[Matt Arsenault via cfe-commits]

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@@ -0,0 +1,21 @@
+// TYPE sign(TYPE x) {
+//   if (isnan(x)) {
+//     return 0.0F;
+//   }
+//   if (x > 0.0F) {
+//     return 1.0F;
+//   }
+//   if (x < 0.0F) {
+//     return -1.0F;
+//   }
+//   return x; /* -0.0 or +0.0 */
+// }
+_CLC_DEF _CLC_OVERLOAD __CLC_GENTYPE __clc_sign(__CLC_GENTYPE x) {
+  __CLC_BIT_INTN x_isnan = __clc_isnan(x);
+  __CLC_BIT_INTN x_isgreater_zero = x > __CLC_FP_LIT(0.0);
+  __CLC_BIT_INTN x_isless_zero = x < __CLC_FP_LIT(0.0);
+  __CLC_GENTYPE sel0 = __clc_select(x, __CLC_FP_LIT(1.0), x_isgreater_zero);
+  __CLC_GENTYPE sel1 = __clc_select(sel0, __CLC_FP_LIT(-1.0), x_isless_zero);
+  __CLC_GENTYPE sel2 = __clc_select(sel1, __CLC_FP_LIT(0.0), x_isnan);
+  return sel2;
+}
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arsenm wrote:

The CTS isn't going to care about the sign bit of nan as it's meaningless. Alive needs to care about getting the signbit handling correct for nan in copysign, but we don't need it to (i.e. it doesn't matter it's not giving bit-identical results to the other implementation) 

https://github.com/llvm/llvm-project/pull/115699