diff --git a/manual/arith.texi b/manual/arith.texi
index dec12a0..1f13769 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -2990,23 +2990,45 @@ double} is a separate type).
 These functions have been GNU extensions and are new to @w{ISO C99}.
 @end deftypefun
 
+@comment stdlib.h
+@comment ISO/IEC TS 18661-3
+@deftypefun _FloatN strtofN (const char *@var{string}, char **@var{tailptr})
+@deftypefunx _FloatNx strtofN (const char *@var{string}, char **@var{tailptr})
+@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
+These functions are like @code{strtod}, except for the return type.
+
+They were introduced in @w{ISO/IEC TS 18661-3} and are available on machines
+that support the related types, as described in @ref{Mathematics}.
+@end deftypefun
+
 @comment wchar.h
 @comment ISO
 @deftypefun double wcstod (const wchar_t *restrict @var{string}, wchar_t **restrict @var{tailptr})
-@comment stdlib.h
+@comment wchar.h
 @comment ISO
 @deftypefunx float wcstof (const wchar_t *@var{string}, wchar_t **@var{tailptr})
-@comment stdlib.h
+@comment wchar.h
 @comment ISO
 @deftypefunx {long double} wcstold (const wchar_t *@var{string}, wchar_t **@var{tailptr})
+@comment wchar.h
+@deftypefunx _FloatN wcstofN (const wchar_t *@var{string}, wchar_t **@var{tailptr})
+@deftypefunx _FloatNx wcstofNx (const wchar_t *@var{string}, wchar_t **@var{tailptr})
 @safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
-The @code{wcstod}, @code{wcstof}, and @code{wcstol} functions are
-equivalent in nearly all aspect to the @code{strtod}, @code{strtof}, and
-@code{strtold} functions but it handles wide character string.
+The @code{wcstod}, @code{wcstof}, @code{wcstol}, @code{wcstof@var{N}},
+and @code{wcstof@var{N}x} functions are equivalent in nearly all aspect
+to the @code{strtod}, @code{strtof}, @code{strtold},
+@code{strtof@var{N}}, and @code{strtof@var{N}x} functions but they
+handle wide character strings.
 
 The @code{wcstod} function was introduced in @w{Amendment 1} of @w{ISO
 C90}.  The @code{wcstof} and @code{wcstold} functions were introduced in
 @w{ISO C99}.
+
+The @code{wcstof@var{N}} and @code{wcstof@var{N}x} functions are not in
+any standard, but are added to provide completeness for the
+non-deprecated interface of wide character string to floating-point
+conversion function.  They are only available on machines that support
+the related types as described in @ref{Mathematics}.
 @end deftypefun
 
 @comment stdlib.h
@@ -3064,6 +3086,19 @@ has been completely written if and only if the returned value is less than
 These functions were introduced by ISO/IEC TS 18661-1.
 @end deftypefun
 
+@comment stdlib.h
+@comment ISO/IEC TS 18661-3
+@deftypefun int strfromfN (char *restrict @var{string}, size_t @var{size}, const char *restrict @var{format}, _Float@var{N} @var{value})
+@deftypefunx int strfromfNx (char *restrict @var{string}, size_t @var{size}, const char *restrict @var{format}, _Float@var{N}x @var{value})
+@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
+@comment this function depends on __printf_fp and __printf_fphex, which are
+@comment AS-unsafe (ascuheap) and AC-unsafe (acsmem).
+These functions are like @code{strfromd}, except for the type of @var{value}.
+
+They were introduced in @w{ISO/IEC TS 18661-3} and are available on machines
+that support the related types, as described in @ref{Mathematics}.
+@end deftypefun
+
 @node System V Number Conversion
 @section Old-fashioned System V number-to-string functions
 
diff --git a/manual/math.texi b/manual/math.texi
index 69a0ace..a335917 100644
--- a/manual/math.texi
+++ b/manual/math.texi
@@ -53,6 +53,17 @@ usually wise to pick the narrowest type that can accommodate your data.
 Not all machines have a distinct @code{long double} type; it may be the
 same as @code{double}.
 
+On some machines, @theglibc{} also provides @code{_Float@var{N}} and
+@code{_Float@var{N}x} types.  These types are defined in @w{ISO/IEC
+18661-3}, which extends @w{ISO C} and defines floating-point types that
+are not machine-dependent.  When such a type, e.g.  @code{_Float128}, is
+supported by @theglibc{}, extra variants for most of the mathematical
+functions provided for @code{double}, @code{float}, and @code{long
+double} are also provided for the supported type.
+
+Currently, support for @code{_Float@var{N}} or @code{_Float@var{N}x}
+types is not provided for any machine.
+
 @menu
 * Mathematical Constants::      Precise numeric values for often-used
                                  constants.
