[wasm] Int64Lowering of FXXXConvertI64 instructions.

src/wasm/wasm-external-refs.h

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WASM_EXTERNAL_REFS_H
+#define WASM_EXTERNAL_REFS_H
+
+namespace v8 {
+namespace internal {
+namespace wasm {
+
+static void f32_trunc_wrapper(float* param) { *param = truncf(*param); }
+
+static void f32_floor_wrapper(float* param) { *param = floorf(*param); }
+
+static void f32_ceil_wrapper(float* param) { *param = ceilf(*param); }
+
+static void f32_nearest_int_wrapper(float* param) {
+  *param = nearbyintf(*param);
+}
+
+static void f64_trunc_wrapper(double* param) { *param = trunc(*param); }
+
+static void f64_floor_wrapper(double* param) { *param = floor(*param); }
+
+static void f64_ceil_wrapper(double* param) { *param = ceil(*param); }
+
+static void f64_nearest_int_wrapper(double* param) {
+  *param = nearbyint(*param);
+}
+
+static void int64_to_float32_wrapper(int64_t* input, float* output) {
+  *output = static_cast<float>(*input);
+}
+
+static void uint64_to_float32_wrapper(uint64_t* input, float* output) {
+#if V8_CC_MSVC
+  // With MSVC we use static_cast<float>(uint32_t) instead of
+  // static_cast<float>(uint64_t) to achieve round-to-nearest-ties-even
+  // semantics. The idea is to calculate
+  // static_cast<float>(high_word) * 2^32 + static_cast<float>(low_word). To
+  // achieve proper rounding in all cases we have to adjust the high_word
+  // with a "rounding bit" sometimes. The rounding bit is stored in the LSB of
+  // the high_word if the low_word may affect the rounding of the high_word.
+  uint32_t low_word = static_cast<uint32_t>(*input & 0xffffffff);
+  uint32_t high_word = static_cast<uint32_t>(*input >> 32);
+
+  float shift = static_cast<float>(1ull << 32);
+  // If the MSB of the high_word is set, then we make space for a rounding bit.
+  if (high_word < 0x80000000) {
+    high_word <<= 1;
+    shift = static_cast<float>(1ull << 31);
+  }
+
+  if ((high_word & 0xfe000000) && low_word) {
+    // Set the rounding bit.
+    high_word |= 1;
+  }
+
+  float result = static_cast<float>(high_word);
+  result *= shift;
+  result += static_cast<float>(low_word);
+  *output = result;
+
+#else
+  *output = static_cast<float>(*input);
+#endif
+}
+
+static void int64_to_float64_wrapper(int64_t* input, double* output) {
+  *output = static_cast<double>(*input);
+}
+
+static void uint64_to_float64_wrapper(uint64_t* input, double* output) {
+#if V8_CC_MSVC
+  // With MSVC we use static_cast<double>(uint32_t) instead of
+  // static_cast<double>(uint64_t) to achieve round-to-nearest-ties-even
+  // semantics. The idea is to calculate
+  // static_cast<double>(high_word) * 2^32 + static_cast<double>(low_word).
+  uint32_t low_word = static_cast<uint32_t>(*input & 0xffffffff);
+  uint32_t high_word = static_cast<uint32_t>(*input >> 32);
+
+  double shift = static_cast<double>(1ull << 32);
+
+  double result = static_cast<double>(high_word);
+  result *= shift;
+  result += static_cast<double>(low_word);
+  *output = result;
+
+#else
+  *output = static_cast<double>(*input);
+#endif
+}
+
+}  // namespace wasm
+}  // namespace internal
+}  // namespace v8
+
+#endif