[compiler-rt] [compiler-rt][ARM] Optimized mulsf3 and divsf3 (PR #161546)

[Saleem Abdulrasool via llvm-commits]

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@@ -0,0 +1,62 @@
+//===-- fnorm2.c - Handle single-precision denormal inputs to binary op ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This helper function is available for use by single-precision float
+// arithmetic implementations, to handle denormal inputs on entry by
+// renormalizing the mantissa and modifying the exponent to match.
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdint.h>
+
+// Structure containing the function's inputs and outputs.
+//
+// On entry: a, b are two input floating-point numbers, still in IEEE 754
+// encoding. expa and expb are the 8-bit exponents of those numbers, extracted
+// and shifted down to the low 8 bits of the word, with no other change.
+// Neither value should be zero, or have the maximum exponent (indicating an
+// infinity or NaN).
+//
+// On exit: each of a and b contains the mantissa of the input value, with the
+// leading 1 bit made explicit, and shifted up to the top of the word. If expa
+// was zero (indicating that a was denormal) then it is now represented as a
+// normalized number with an out-of-range exponent (zero or negative). The same
+// applies to expb and b.
+struct fnorm2 {
+  uint32_t a, b, expa, expb;
+};
+
+void __compiler_rt_fnorm2(struct fnorm2 *values) {
+  // Shift the mantissas of a and b to the right place to follow a leading 1 in
+  // the top bit, if there is one.
+  values->a <<= 8;
+  values->b <<= 8;
+
+  // Test if a is denormal.
+  if (values->expa == 0) {
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compnerd wrote:

Future enhancement idea: extract the adjustment into a helper and share across the two values.

https://github.com/llvm/llvm-project/pull/161546