Use the fast_float library to parse floating-point numbers

This commit brings in the amalgamated header of the fast_float library,
and applies it to our uses of sscanf with %f.

This library is locale-free, and does not incur the performance penalty of
using a thread locale RAII class.

Fixes AcademySoftwareFoundation#297
Fixes AcademySoftwareFoundation#379
Fixes AcademySoftwareFoundation#1022

THIRD-PARTY.md

@@ -229,4 +229,56 @@ England
 
 ---------------------------------------------------------------------
 
+fast_float number parsing library, courtesy of The fast_float authors.
+https://github.com/fastfloat/fast_float/
+
+Licensed under either of Apache License, Version 2.0 or MIT license at your option.
+Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this repository by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
+
+(the terms of the Apache License follow)
+
+  Copyright 2020 The fast_float 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.
+
+(the terms of the MIT License follow)
+
+  Copyright 2020 The fast_float authors 
+
+  Permission is hereby granted, free of charge, to any
+  person obtaining a copy of this software and associated
+  documentation files (the "Software"), to deal in the
+  Software without restriction, including without
+  limitation the rights to use, copy, modify, merge,
+  publish, distribute, sublicense, and/or sell copies of
+  the Software, and to permit persons to whom the Software
+  is furnished to do so, subject to the following
+  conditions:
+
+  The above copyright notice and this permission notice
+  shall be included in all copies or substantial portions
+  of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+  ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+  TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+  SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+  IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+  DEALINGS IN THE SOFTWARE.
+
+---------------------------------------------------------------------
+
 If we have left anything out, it is unintentional. Please let us know.

ext/CMakeLists.txt

@@ -6,3 +6,5 @@
 
 # Sample ICC (modified)
 add_subdirectory(sampleicc)
+
+add_subdirectory(fast_float)

ext/fast_float/CMakeLists.txt

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright Contributors to the OpenColorIO Project.
+
+# fast_float amalgamated header
+# https://github.com/fastfloat/fast_float
+add_library(fast_float::fast_float INTERFACE IMPORTED GLOBAL)
+set_target_properties(fast_float::fast_float PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES "${CMAKE_CURRENT_SOURCE_DIR}/src/include"
+)

ext/fast_float/README.md

@@ -0,0 +1,12 @@
+fast_float number parsing library: 4x faster than strtod
+========================================================
+
+The fast_float library provides fast header-only implementations for the C++ from_chars
+functions for `float` and `double` types.  These functions convert ASCII strings representing
+decimal values (e.g., `1.3e10`) into binary types. We provide exact rounding (including
+round to even). In our experience, these `fast_float` functions many times faster than comparable number-parsing functions from existing C++ standard libraries.
+
+This is the amalgamated header of version 3.1.0, available at:
+
+https://github.com/fastfloat/fast_float/releases/tag/v3.1.0
+