diff --git a/bits/flt-eval-method.h b/bits/flt-eval-method.h
new file mode 100644
index 0000000..8ecd6a6
--- /dev/null
+++ b/bits/flt-eval-method.h
@@ -0,0 +1,42 @@
+/* Define __GLIBC_FLT_EVAL_METHOD.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_H
+# error "Never use <bits/flt-eval-method.h> directly; include <math.h> instead."
+#endif
+
+/* __GLIBC_FLT_EVAL_METHOD is the value of FLT_EVAL_METHOD used to
+   determine the evaluation method typedefs such as float_t and
+   double_t.  It must be a value from C11 or TS 18661-3:2015, and not
+   -1.  */
+
+/* In the default version of this header, follow __FLT_EVAL_METHOD__.
+   -1 is mapped to 2 (considering evaluation as long double to be a
+   conservatively safe assumption), and if __FLT_EVAL_METHOD__ is not
+   defined then assume there is no excess precision and use the value
+   0.  */
+
+#ifdef __FLT_EVAL_METHOD__
+# if __FLT_EVAL_METHOD__ == -1
+#  define __GLIBC_FLT_EVAL_METHOD	2
+# else
+#  define __GLIBC_FLT_EVAL_METHOD	__FLT_EVAL_METHOD__
+# endif
+#else
+# define __GLIBC_FLT_EVAL_METHOD	0
+#endif
diff --git a/bits/mathdef.h b/bits/mathdef.h
index d557d08..6dedc51 100644
--- a/bits/mathdef.h
+++ b/bits/mathdef.h
@@ -22,13 +22,6 @@
 #if defined  __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* Expressions are evaluated with the range and precision of their
-   type.  */
-typedef float float_t;		/* `float' expressions are evaluated as
-				   `float'.  */
-typedef double double_t;	/* `double' expressions are evaluated as
-				   `double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	2147483647
diff --git a/math/Makefile b/math/Makefile
index e84f86a..576e108 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -27,7 +27,8 @@ headers		:= math.h bits/mathcalls.h bits/mathinline.h bits/huge_val.h \
 		   fpu_control.h complex.h bits/cmathcalls.h fenv.h \
 		   bits/fenv.h bits/fenvinline.h bits/mathdef.h tgmath.h \
 		   bits/math-finite.h bits/math-vector.h \
-		   bits/libm-simd-decl-stubs.h bits/iscanonical.h
+		   bits/libm-simd-decl-stubs.h bits/iscanonical.h \
+		   bits/flt-eval-method.h
 
 # FPU support code.
 aux		:= setfpucw fpu_control
diff --git a/math/math.h b/math/math.h
index 75ccfc3..70bf8e5 100644
--- a/math/math.h
+++ b/math/math.h
@@ -54,13 +54,51 @@ __BEGIN_DECLS
 # endif
 #endif
 
-/* Get the architecture specific values describing the floating-point
-   evaluation.  The following symbols will get defined:
+/* Get __GLIBC_FLT_EVAL_METHOD.  */
+#include <bits/flt-eval-method.h>
+
+#ifdef __USE_ISOC99
+/* Define the following typedefs.
 
     float_t	floating-point type at least as wide as `float' used
 		to evaluate `float' expressions
     double_t	floating-point type at least as wide as `double' used
 		to evaluate `double' expressions
+*/
+# if __GLIBC_FLT_EVAL_METHOD == 0 || __GLIBC_FLT_EVAL_METHOD == 16
+typedef float float_t;
+typedef double double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 1
+typedef double float_t;
+typedef double double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 2
+typedef long double float_t;
+typedef long double double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 32
+typedef _Float32 float_t;
+typedef double double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 33
+typedef _Float32x float_t;
+typedef _Float32x double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 64
+typedef _Float64 float_t;
+typedef _Float64 double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 65
+typedef _Float64x float_t;
+typedef _Float64x double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 128
+typedef _Float128 float_t;
+typedef _Float128 double_t;
+# elif __GLIBC_FLT_EVAL_METHOD == 129
+typedef _Float128x float_t;
+typedef _Float128x double_t;
+# else
+#  error "Unknown __GLIBC_FLT_EVAL_METHOD"
+# endif
+#endif
+
+/* Get the architecture specific values describing the floating-point
+   evaluation.  The following symbols will get defined:
 
     FP_FAST_FMA
     FP_FAST_FMAF
diff --git a/sysdeps/aarch64/bits/mathdef.h b/sysdeps/aarch64/bits/mathdef.h
index db992fc..2b55b59 100644
--- a/sysdeps/aarch64/bits/mathdef.h
+++ b/sysdeps/aarch64/bits/mathdef.h
@@ -23,12 +23,6 @@
 #if defined  __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* GCC does not promote `float' values to `double'.  */
-typedef float float_t;		/* `float' expressions are evaluated as
-				   `float'.  */
-typedef double double_t;	/* `double' expressions are evaluated as
-				   `double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	(2147483647)
diff --git a/sysdeps/alpha/bits/mathdef.h b/sysdeps/alpha/bits/mathdef.h
index ed70ad8..fbca194 100644
--- a/sysdeps/alpha/bits/mathdef.h
+++ b/sysdeps/alpha/bits/mathdef.h
@@ -25,10 +25,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* Alpha has "float" and "double" operations.  */
-typedef float float_t;    /* float expressions are evaluated as float.  */
-typedef double double_t;  /* double expressions are evaluated as double.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0     (-2147483647)
 # define FP_ILOGBNAN   (2147483647)
diff --git a/sysdeps/arm/bits/mathdef.h b/sysdeps/arm/bits/mathdef.h
index ae0bcb7..68c96f0 100644
--- a/sysdeps/arm/bits/mathdef.h
+++ b/sysdeps/arm/bits/mathdef.h
@@ -22,12 +22,6 @@
 #if defined  __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* GCC does not promote `float' values to `double'.  */
-typedef float float_t;		/* `float' expressions are evaluated as
-				   `float'.  */
-typedef double double_t;	/* `double' expressions are evaluated as
-				   `double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	(2147483647)
diff --git a/sysdeps/hppa/fpu/bits/mathdef.h b/sysdeps/hppa/fpu/bits/mathdef.h
index 99c9cff..24b67b2 100644
--- a/sysdeps/hppa/fpu/bits/mathdef.h
+++ b/sysdeps/hppa/fpu/bits/mathdef.h
@@ -22,12 +22,6 @@
 #if defined  __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* GCC does not promote `float' values to `double'.  */
-typedef float float_t;		/* `float' expressions are evaluated as
-				   `float'.  */
-typedef double double_t;	/* `double' expressions are evaluated as
-				   `double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	(2147483647)
diff --git a/sysdeps/ia64/bits/mathdef.h b/sysdeps/ia64/bits/mathdef.h
index 5a31bd3..44a7642 100644
--- a/sysdeps/ia64/bits/mathdef.h
+++ b/sysdeps/ia64/bits/mathdef.h
@@ -22,13 +22,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* The IA-64 architecture computes values with the precision of the
-   used type.  */
-typedef float float_t;		/* `float' expressions are evaluated as
-				   `float'.  */
-typedef double double_t;	/* `double' expressions are evaluated as
-				   `double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647 - 1)
 # define FP_ILOGBNAN	2147483647
diff --git a/sysdeps/m68k/m680x0/bits/flt-eval-method.h b/sysdeps/m68k/m680x0/bits/flt-eval-method.h
new file mode 100644
index 0000000..b2a38ac
--- /dev/null
+++ b/sysdeps/m68k/m680x0/bits/flt-eval-method.h
@@ -0,0 +1,25 @@
+/* Define __GLIBC_FLT_EVAL_METHOD.  M68K version.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_H
+# error "Never use <bits/flt-eval-method.h> directly; include <math.h> instead."
+#endif
+
+/* The m68k FPUs evaluate all values in the 96-bit floating-point
+   format which is also available for the user as 'long double'.  */
+#define __GLIBC_FLT_EVAL_METHOD	2
diff --git a/sysdeps/m68k/m680x0/bits/mathdef.h b/sysdeps/m68k/m680x0/bits/mathdef.h
index a550938..702bd0e 100644
--- a/sysdeps/m68k/m680x0/bits/mathdef.h
+++ b/sysdeps/m68k/m680x0/bits/mathdef.h
@@ -22,14 +22,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* The m68k FPUs evaluate all values in the 96 bit floating-point format
-   which is also available for the user as `long double'.  Therefore we
-   define: */
-typedef long double float_t;	/* `float' expressions are evaluated as
-				   `long double'.  */
-typedef long double double_t;	/* `double' expressions are evaluated as
-				   `long double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647 - 1)
 # define FP_ILOGBNAN	(2147483647)
diff --git a/sysdeps/mips/bits/mathdef.h b/sysdeps/mips/bits/mathdef.h
index 3a11627..74abf97 100644
--- a/sysdeps/mips/bits/mathdef.h
+++ b/sysdeps/mips/bits/mathdef.h
@@ -24,12 +24,6 @@
 #if defined  __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* MIPS has `float' and `double' operations.  */
-typedef float float_t;		/* `float' expressions are evaluated as
-				   `float'.  */
-typedef double double_t;	/* `double' expressions are evaluated as
-				   `double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	2147483647
diff --git a/sysdeps/powerpc/bits/mathdef.h b/sysdeps/powerpc/bits/mathdef.h
index d4dd4b5..debb5a5 100644
--- a/sysdeps/powerpc/bits/mathdef.h
+++ b/sysdeps/powerpc/bits/mathdef.h
@@ -29,10 +29,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* PowerPC has both `float' and `double' arithmetic.  */
-typedef float float_t;
-typedef double double_t;
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	(2147483647)
diff --git a/sysdeps/s390/bits/flt-eval-method.h b/sysdeps/s390/bits/flt-eval-method.h
new file mode 100644
index 0000000..5793175
--- /dev/null
+++ b/sysdeps/s390/bits/flt-eval-method.h
@@ -0,0 +1,24 @@
+/* Define __GLIBC_FLT_EVAL_METHOD.  S/390 version.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_H
+# error "Never use <bits/flt-eval-method.h> directly; include <math.h> instead."
+#endif
+
+/* This value is used because of a historical mistake.  */
+#define __GLIBC_FLT_EVAL_METHOD	1
diff --git a/sysdeps/s390/bits/mathdef.h b/sysdeps/s390/bits/mathdef.h
index 8c47ade..5ad04ae 100644
--- a/sysdeps/s390/bits/mathdef.h
+++ b/sysdeps/s390/bits/mathdef.h
@@ -22,13 +22,6 @@
 #if defined  __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* Normally, there is no long double type and the `float' and `double'
-   expressions are evaluated as `double'.  */
-typedef double float_t;		/* `float' expressions are evaluated as
-				   `double'.  */
-typedef double double_t;	/* `double' expressions are evaluated as
-				   `double'.  */
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	2147483647
diff --git a/sysdeps/sh/sh4/bits/mathdef.h b/sysdeps/sh/sh4/bits/mathdef.h
index 21ce094..f3ee287 100644
--- a/sysdeps/sh/sh4/bits/mathdef.h
+++ b/sysdeps/sh/sh4/bits/mathdef.h
@@ -29,10 +29,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* SH has both `float' and `double' arithmetic.  */
-typedef float float_t;
-typedef double double_t;
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-0x7fffffff)
 # define FP_ILOGBNAN	0x7fffffff
diff --git a/sysdeps/sparc/bits/mathdef.h b/sysdeps/sparc/bits/mathdef.h
index 94a102a..55a3530 100644
--- a/sysdeps/sparc/bits/mathdef.h
+++ b/sysdeps/sparc/bits/mathdef.h
@@ -27,10 +27,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* SPARC has both `float' and `double' arithmetic.  */
-typedef float float_t;
-typedef double double_t;
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0       (-2147483647)
 # define FP_ILOGBNAN     (2147483647)
diff --git a/sysdeps/tile/bits/mathdef.h b/sysdeps/tile/bits/mathdef.h
index 2db81b4..8ed7ac4 100644
--- a/sysdeps/tile/bits/mathdef.h
+++ b/sysdeps/tile/bits/mathdef.h
@@ -23,10 +23,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-/* "float" and "double" expressions evaluated as "float" and "double". */
-typedef float float_t;
-typedef double double_t;
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647)
 # define FP_ILOGBNAN	(2147483647)
diff --git a/sysdeps/x86/bits/flt-eval-method.h b/sysdeps/x86/bits/flt-eval-method.h
new file mode 100644
index 0000000..674f2fc
--- /dev/null
+++ b/sysdeps/x86/bits/flt-eval-method.h
@@ -0,0 +1,33 @@
+/* Define __GLIBC_FLT_EVAL_METHOD.  x86 version.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_H
+# error "Never use <bits/flt-eval-method.h> directly; include <math.h> instead."
+#endif
+
+#ifdef __FLT_EVAL_METHOD__
+# if __FLT_EVAL_METHOD__ == -1
+#  define __GLIBC_FLT_EVAL_METHOD	2
+# else
+#  define __GLIBC_FLT_EVAL_METHOD	__FLT_EVAL_METHOD__
+# endif
+#elif defined __x86_64__
+# define __GLIBC_FLT_EVAL_METHOD	0
+#else
+# define __GLIBC_FLT_EVAL_METHOD	2
+#endif
diff --git a/sysdeps/x86/bits/mathdef.h b/sysdeps/x86/bits/mathdef.h
index 9423a7f..2f0025c 100644
--- a/sysdeps/x86/bits/mathdef.h
+++ b/sysdeps/x86/bits/mathdef.h
@@ -22,23 +22,6 @@
 #if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
 # define _MATH_H_MATHDEF	1
 
-# if ((defined __x86_64__ && !defined __FLT_EVAL_METHOD__)		\
-      || (defined __FLT_EVAL_METHOD__ && __FLT_EVAL_METHOD__ == 0))
-/* The x86-64 architecture computes values with the precission of the
-   used type.  Similarly for -m32 -mfpmath=sse.  */
-typedef float float_t;		/* `float' expressions are evaluated as `float'.  */
-typedef double double_t;	/* `double' expressions are evaluated
-				   as `double'.  */
-# else
-/* The ix87 FPUs evaluate all values in the 80 bit floating-point format
-   which is also available for the user as `long double'.  Therefore we
-   define:  */
-typedef long double float_t;	/* `float' expressions are evaluated as
-				   `long double'.  */
-typedef long double double_t;	/* `double' expressions are evaluated as
-				   `long double'.  */
-# endif
-
 /* The values returned by `ilogb' for 0 and NaN respectively.  */
 # define FP_ILOGB0	(-2147483647 - 1)
 # define FP_ILOGBNAN	(-2147483647 - 1)
