Bug 1358149 add a header to substitute fdlibm math functions for inexact system library functions r=arai

This provides a way to use fdlibm from third party C code without
modification, such as media/ffvpx, which is regularly updated and so this
avoids patching the vendored library.

Differential Revision: https://phabricator.services.mozilla.com/D185780

modules/fdlibm/inexact-math-override/math.h

@@ -0,0 +1,86 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * This is intended for use only with vendored C libraries where editing the
+ * source files to explicitly use fdblim is not desirable due to maintenance
+ * burden.  cmath for C++ is not supported.
+ *
+ * Use LOCAL_INCLUDES += ['/modules/fdlibm/inexact-math-override'] to
+ * substitute fdlibm math functions for inexact functions in system libraries.
+ *
+ * This is intended to remove fingerprinting entropy due to variations in
+ * return values from system libaries.  Exact functions are not substituted
+ * because these are expected to return consistent results regardless of
+ * implementation.  sqrt() is considered exact as correct rounding is required
+ * by IEEE-754.
+ */
+
+#ifndef MODULES_FDLIBM_INEXACT_MATH_OVERRIDE_MATH_H_
+#define MODULES_FDLIBM_INEXACT_MATH_OVERRIDE_MATH_H_
+
+#include_next <math.h>
+
+#include <fdlibm.h>
+
+#define acos fdlibm_acos
+#define acosf fdlibm_acosf
+#define asin fdlibm_asin
+#define asinf fdlibm_asinf
+#define atan fdlibm_atan
+#define atanf fdlibm_atanf
+#define atan2 fdlibm_atan2
+#define cos fdlibm_cos
+#define cosf fdlibm_cosf
+#define sin fdlibm_sin
+#define sinf fdlibm_sinf
+#define tan fdlibm_tan
+#define tanf fdlibm_tanf
+#define cosh fdlibm_cosh
+#define sinh fdlibm_sinh
+#define tanh fdlibm_tanh
+#define exp fdlibm_exp
+#define expf fdlibm_expf
+#define exp2 fdlibm_exp2
+#define exp2f fdlibm_exp2f
+#define log fdlibm_log
+#define logf fdlibm_logf
+#define log10 fdlibm_log10
+#define log10f fdlibm_log10f
+#define pow fdlibm_pow
+#define powf fdlibm_powf
+#define acosh fdlibm_acosh
+#define asinh fdlibm_asinh
+#define atanh fdlibm_atanh
+#define cbrt fdlibm_cbrt
+#define expm1 fdlibm_expm1
+#define hypot fdlibm_hypot
+#define hypotf fdlibm_hypotf
+#define log1p fdlibm_log1p
+#define log2 fdlibm_log2
+
+// These functions are not yet vendored from fdlibm but are defined here to
+// catch any uses that would imply that they should be vendored.
+#define coshf fdlibm_coshf
+#define sinhf fdlibm_sinhf
+#define tanhf fdlibm_tanhf
+#define acoshf fdlibm_acoshf
+#define asinhf fdlibm_asinhf
+#define atanhf fdlibm_atanhf
+#define cbrtf fdlibm_cbrtf
+#define expm1f fdlibm_expm1f
+#define log1pf fdlibm_log1pf
+#define log2f fdlibm_log2f
+#define erf fdlibm_erf
+#define erff fdlibm_erff
+#define erfc fdlibm_erfc
+#define erfcf fdlibm_erfcf
+#define tgamma fdlibm_tgamma
+#define tgammaf fdlibm_tgammaf
+#define lgamma fdlibm_lgamma
+#define lgammaf fdlibm_lgammaf
+
+#endif  // MODULES_FDLIBM_INEXACT_MATH_OVERRIDE_MATH_H_