[glibc] Amend grammar and add a description

[Carlos O'Donell]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=0a3fce86eecd4aa1df4b0695b4aecc314268181c

commit 0a3fce86eecd4aa1df4b0695b4aecc314268181c
Author: Jonny Grant <jg@jguk.org>
Date:   Mon Oct 26 14:55:14 2020 +0000

    Amend grammar and add a description
    
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 string/byteswap.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/string/byteswap.h b/string/byteswap.h
index ca600d863d..8f6939717c 100644
--- a/string/byteswap.h
+++ b/string/byteswap.h
@@ -1,4 +1,5 @@
-/* Copyright (C) 1997-2020 Free Software Foundation, Inc.
+/* Swap byte order for 16, 32 and 64 bit values
+   Copyright (C) 1997-2020 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
@@ -24,10 +25,10 @@
 #include <bits/byteswap.h>
 
 
-/* The following definitions must all be macros since otherwise some
+/* The following definitions must all be macros, otherwise some
    of the possible optimizations are not possible.  */
 
-/* Return a value with all bytes in the 16 bit argument swapped.  */
+/* Return a value with both bytes in the 16 bit argument swapped.  */
 #define bswap_16(x) __bswap_16 (x)
 
 /* Return a value with all bytes in the 32 bit argument swapped.  */