Add a utils/string_stream class.

This CL adds `utils::StringStream`. This is a wrapper over
std::stringstream which forces the locale to always be `classic`. The
logic to format floats and doubles as expected is moved from
`float_to_string` and handled in the StreamStream. This will make all of
our float emission the same.

Bug: tint:1686
Change-Id: If51868f577580d3ea6ab94d3910393e239fd55e4
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/121800
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/tint/BUILD.gn

@@ -221,6 +221,8 @@ libtint_source_set("libtint_base_src") {
     "utils/slice.h",
     "utils/string.cc",
     "utils/string.h",
+    "utils/string_stream.cc",
+    "utils/string_stream.h",
     "utils/unique_allocator.h",
     "utils/unique_vector.h",
     "utils/vector.h",
@@ -1559,6 +1561,7 @@ if (tint_build_unittests) {
       "utils/reverse_test.cc",
       "utils/scoped_assignment_test.cc",
       "utils/slice_test.cc",
+      "utils/string_stream_test.cc",
       "utils/string_test.cc",
       "utils/transform_test.cc",
       "utils/unique_allocator_test.cc",

src/tint/CMakeLists.txt

@@ -530,6 +530,8 @@ list(APPEND TINT_LIB_SRCS
   utils/slice.h
   utils/string.cc
   utils/string.h
+  utils/string_stream.cc
+  utils/string_stream.h
   utils/unique_allocator.h
   utils/unique_vector.h
   utils/vector.h
@@ -985,6 +987,7 @@ if(TINT_BUILD_TESTS)
     utils/reverse_test.cc
     utils/scoped_assignment_test.cc
     utils/slice_test.cc
+    utils/string_stream_test.cc
     utils/string_test.cc
     utils/transform_test.cc
     utils/unique_allocator_test.cc

src/tint/utils/string_stream.cc

@@ -0,0 +1,27 @@
+// Copyright 2023 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/tint/utils/string_stream.h"
+
+namespace tint::utils {
+
+StringStream::StringStream() {
+    sstream_.flags(sstream_.flags() | std::ios_base::showpoint | std::ios_base::fixed);
+    sstream_.imbue(std::locale::classic());
+    sstream_.precision(9);
+}
+
+StringStream::~StringStream() = default;
+
+}  // namespace tint::utils

src/tint/utils/string_stream.h

@@ -0,0 +1,105 @@
+// Copyright 2023 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TINT_UTILS_STRING_STREAM_H_
+#define SRC_TINT_UTILS_STRING_STREAM_H_
+
+#include <functional>
+#include <limits>
+#include <sstream>
+#include <string>
+
+namespace tint::utils {
+
+/// Stringstream wrapper which automatically resets the locale and sets floating point emission
+/// settings needed for Tint.
+class StringStream {
+  public:
+    /// Constructor
+    StringStream();
+    /// Destructor
+    ~StringStream();
+
+    /// Emit `value` to the stream
+    /// @param value the value to emit
+    /// @returns a reference to this
+    template <typename T,
+              typename std::enable_if<!std::is_floating_point<T>::value>::type* = nullptr>
+    StringStream& operator<<(const T& value) {
+        sstream_ << value;
+        return *this;
+    }
+
+    /// Emit `value` to the stream
+    /// @param value the value to emit
+    /// @returns a reference to this
+    template <typename T,
+              typename std::enable_if<std::is_floating_point<T>::value>::type* = nullptr>
+    StringStream& operator<<(const T& value) {
+        // Try printing the float in fixed point, with a smallish limit on the precision
+        std::stringstream fixed;
+        fixed.flags(fixed.flags() | std::ios_base::showpoint | std::ios_base::fixed);
+        fixed.imbue(std::locale::classic());
+        fixed.precision(9);
+        fixed << value;
+
+        std::string str = fixed.str();
+
+        // If this string can be parsed without loss of information, use it.
+        // (Use double here to dodge a bug in older libc++ versions which would incorrectly read
+        // back FLT_MAX as INF.)
+        double roundtripped;
+        fixed >> roundtripped;
+
+        auto float_equal_no_warning = std::equal_to<T>();
+        if (float_equal_no_warning(value, static_cast<T>(roundtripped))) {
+            while (str.length() >= 2 && str[str.size() - 1] == '0' && str[str.size() - 2] != '.') {
+                str.pop_back();
+            }
+
+            sstream_ << str;
+            return *this;
+        }
+
+        // Resort to scientific, with the minimum precision needed to preserve the whole float
+        std::stringstream sci;
+        sci.imbue(std::locale::classic());
+        sci.precision(std::numeric_limits<T>::max_digits10);
+        sci << value;
+        sstream_ << sci.str();
+
+        return *this;
+    }
+
+    /// The callback to emit a `endl` to the stream
+    using StdEndl = std::ostream& (*)(std::ostream&);
+
+    /// @param manipulator the callback to emit too
+    /// @returns a reference to this
+    StringStream& operator<<(StdEndl manipulator) {
+        // call the function, and return it's value
+        manipulator(sstream_);
+        return *this;
+    }
+
+    /// @returns the string contents of the stream
+    std::string str() const { return sstream_.str(); }
+
+  private:
+    std::stringstream sstream_;
+};
+
+}  // namespace tint::utils
+
+#endif  // SRC_TINT_UTILS_STRING_STREAM_H_

src/tint/utils/string_stream_test.cc

@@ -0,0 +1,117 @@
+// Copyright 2023 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/tint/utils/string_stream.h"
+
+#include <math.h>
+#include <cstring>
+#include <limits>
+
+#include "gtest/gtest.h"
+
+namespace tint::utils {
+namespace {
+
+using StringStreamTest = testing::Test;
+
+TEST_F(StringStreamTest, Endl) {
+    StringStream s;
+    s << std::endl;
+    EXPECT_EQ(s.str(), "\n");
+}
+
+TEST_F(StringStreamTest, Zero) {
+    StringStream s;
+    s << 0.0f;
+    EXPECT_EQ(s.str(), "0.0");
+}
+
+TEST_F(StringStreamTest, One) {
+    StringStream s;
+    s << 1.0f;
+    EXPECT_EQ(s.str(), "1.0");
+}
+
+TEST_F(StringStreamTest, MinusOne) {
+    StringStream s;
+    s << -1.0f;
+    EXPECT_EQ(s.str(), "-1.0");
+}
+
+TEST_F(StringStreamTest, Billion) {
+    StringStream s;
+    s << 1e9f;
+    EXPECT_EQ(s.str(), "1000000000.0");
+}
+
+TEST_F(StringStreamTest, Small) {
+    StringStream s;
+    s << std::numeric_limits<float>::epsilon();
+    EXPECT_NE(s.str(), "0.0");
+}
+
+TEST_F(StringStreamTest, Highest) {
+    const auto highest = std::numeric_limits<float>::max();
+    const auto expected_highest = 340282346638528859811704183484516925440.0f;
+
+    if (highest < expected_highest || highest > expected_highest) {
+        GTEST_SKIP() << "std::numeric_limits<float>::max() is not as expected for "
+                        "this target";
+    }
+
+    StringStream s;
+    s << std::numeric_limits<float>::max();
+    EXPECT_EQ(s.str(), "340282346638528859811704183484516925440.0");
+}
+
+TEST_F(StringStreamTest, Lowest) {
+    // Some compilers complain if you test floating point numbers for equality.
+    // So say it via two inequalities.
+    const auto lowest = std::numeric_limits<float>::lowest();
+    const auto expected_lowest = -340282346638528859811704183484516925440.0f;
+    if (lowest < expected_lowest || lowest > expected_lowest) {
+        GTEST_SKIP() << "std::numeric_limits<float>::lowest() is not as expected for "
+                        "this target";
+    }
+
+    StringStream s;
+    s << std::numeric_limits<float>::lowest();
+    EXPECT_EQ(s.str(), "-340282346638528859811704183484516925440.0");
+}
+
+TEST_F(StringStreamTest, Precision) {
+    {
+        StringStream s;
+        s << 1e-8f;
+        EXPECT_EQ(s.str(), "0.00000001");
+    }
+    {
+        StringStream s;
+        s << 1e-9f;
+        EXPECT_EQ(s.str(), "0.000000001");
+    }
+    {
+        StringStream s;
+        s << 1e-10f;
+        EXPECT_EQ(s.str(), "1.00000001e-10");
+    }
+    {
+        StringStream s;
+        s << 1e-20f;
+        EXPECT_EQ(s.str(), "9.99999968e-21");
+    }
+}
+
+}  // namespace
+}  // namespace tint::utils

src/tint/writer/float_to_string.cc

@@ -22,6 +22,7 @@
 #include <sstream>
 
 #include "src/tint/debug.h"
+#include "src/tint/utils/string_stream.h"
 
 namespace tint::writer {
 
@@ -52,35 +53,9 @@ struct Traits<double> {
 
 template <typename F>
 std::string ToString(F f) {
-    // Try printing the float in fixed point, with a smallish limit on the precision
+    utils::StringStream s;
-    std::stringstream fixed;
+    s << f;
-    fixed.flags(fixed.flags() | std::ios_base::showpoint | std::ios_base::fixed);
+    return s.str();
-    fixed.imbue(std::locale::classic());
-    fixed.precision(9);
-    fixed << f;
-    std::string str = fixed.str();
-
-    // If this string can be parsed without loss of information, use it.
-    // (Use double here to dodge a bug in older libc++ versions which would incorrectly read back
-    // FLT_MAX as INF.)
-    double roundtripped;
-    fixed >> roundtripped;
-
-    auto float_equal_no_warning = std::equal_to<F>();
-    if (float_equal_no_warning(f, static_cast<F>(roundtripped))) {
-        while (str.length() >= 2 && str[str.size() - 1] == '0' && str[str.size() - 2] != '.') {
-            str.pop_back();
-        }
-
-        return str;
-    }
-
-    // Resort to scientific, with the minimum precision needed to preserve the whole float
-    std::stringstream sci;
-    sci.imbue(std::locale::classic());
-    sci.precision(std::numeric_limits<F>::max_digits10);
-    sci << f;
-    return sci.str();
 }
 
 template <typename F>