Re: Fix REALLOC_ZERO_BYTES_FREES comment

[Paul Eggert <eggert@cs.ucla.edu>]

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On 4/11/21 11:19 PM, Paul Zimmermann wrote:
> Why not simply the following?
> 
> "Otherwise, realloc (p, 0) should free p and return what malloc (0) would."

Thanks, that is better wording. I installed the attached comment patch, 
which also attempts to address the other points you and Florian made.

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From 9f1bed18f9466ac886addb2f79d8e4c52fb65eb5 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 12 Apr 2021 00:33:15 -0700
Subject: [PATCH] Further fixes for REALLOC_ZERO_BYTES_FREES comment

* malloc/malloc.c (REALLOC_ZERO_BYTES_FREES): Improve comment further.
---
 malloc/malloc.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 0cd3ba78ca..e2d7b1b583 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -346,13 +346,14 @@ __malloc_assert (const char *assertion, const char *file, unsigned int line,
 #define REVEAL_PTR(ptr)  PROTECT_PTR (&ptr, ptr)
 
 /*
-  REALLOC_ZERO_BYTES_FREES controls the behavior of realloc (p, 0)
-  when p is nonnull.  If nonzero, realloc (p, 0) should free p and
-  return NULL.  Otherwise, realloc (p, 0) should do the equivalent
-  of freeing p and returning what malloc (0) would return.
-
-  ISO C17 says the behavior is implementation-defined here; glibc
-  follows historical practice and defines it to be nonzero.
+  The REALLOC_ZERO_BYTES_FREES macro controls the behavior of realloc (p, 0)
+  when p is nonnull.  If the macro is nonzero, the realloc call returns NULL;
+  otherwise, the call returns what malloc (0) would.  In either case,
+  p is freed.  Glibc uses a nonzero REALLOC_ZERO_BYTES_FREES, which
+  implements common historical practice.
+
+  ISO C17 says the realloc call has implementation-defined behavior,
+  and it might not even free p.
 */
 
 #ifndef REALLOC_ZERO_BYTES_FREES
-- 
2.27.0