[libc-commits] [libc] [libc][mathvec] Initial commit for LIBC vector math component (PR #173058)

[Muhammad Bassiouni via libc-commits]

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@@ -0,0 +1,84 @@
+//===-- Implementation header for SIMD expf ---------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_MATHVEC_EXPF_H
+#define LLVM_LIBC_SRC___SUPPORT_MATHVEC_EXPF_H
+
+#include "src/__support/CPP/simd.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/common.h"
+#include "src/__support/mathvec/expf_utils.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace mathvec {
+
+template <size_t N>
+LIBC_INLINE static cpp::simd<double, N> inline_exp(cpp::simd<double, N> x) {
+  static constexpr cpp::simd<double, N> shift = 0x1.800000000ffc0p+46;
+
+  // inv_ln2 = round(1/log(2), D, RN);
+  static constexpr cpp::simd<double, N> inv_ln2 = 0x1.71547652b82fep+0;
+  cpp::simd<double, N> z = shift + x * inv_ln2;
+  cpp::simd<double, N> n = z - shift;
+
+  // ln2_hi = round(log(2), D, RN);
+  // ln2_lo = round(log(2) - ln2_hi, D, RN);
+  static constexpr cpp::simd<double, N> ln2_hi = 0x1.62e42fefa39efp-1;
+  static constexpr cpp::simd<double, N> ln2_lo = 0x1.abc9e3b39803fp-56;
+
+  cpp::simd<double, N> r = x;
+  r = r - n * ln2_hi;
+  r = r - n * ln2_lo;
+
+  // Coefficients of exp approximation, generated by Sollya with:
+  // poly = 1 + x;
+  // for i from 2 to 5 do {
+  //   r = remez(exp(x)-poly(x), 5-i, [-log(2)/128;log(2)/128], x^i, 1e-10);
+  //   c = coeff(roundcoefficients(r, [|D ...|]), 0);
+  //   poly = poly + x^i*c;
+  //   c;
+  // };
+  static constexpr cpp::simd<double, N> c0 = 0x1.fffffffffdbcep-2;
+  static constexpr cpp::simd<double, N> c1 = 0x1.55555555543c2p-3;
+  static constexpr cpp::simd<double, N> c2 = 0x1.555573c64f2e3p-5;
+  static constexpr cpp::simd<double, N> c3 = 0x1.111126b4eff73p-7;
+
+  /* y = exp(r) - 1 ~= r + C0 r^2 + C1 r^3 + C2 r^4 + C3 r^5.  */
+  cpp::simd<double, N> r2 = r * r;
+  cpp::simd<double, N> p01 = c0 + r * c1;
+  cpp::simd<double, N> p23 = c2 + r * c3;
+  cpp::simd<double, N> p04 = p01 + r2 * p23;
+  cpp::simd<double, N> y = r + p04 * r2;
+
+  cpp::simd<uint64_t, N> u = cpp::bit_cast<cpp::simd<uint64_t, N>>(z);
+  cpp::simd<double, N> s = exp_lookup(u);
+  return s + s * y;
+}
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bassiounix wrote:

@Prabhuk I also would like to have your input on static storage inside function body, does it cause the same bloat it did with symbols before? or is it fine to leave them there?

https://github.com/llvm/llvm-project/pull/173058