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Simplify the definition of png_isaligned and avoid compiler warnings

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The following pointer subtraction was unnecessary:
((const char*)(ptr)-(const char*)0)

In order to avoid further warnings about casting a wide pointer type
to a narrower integer type, we cast the pointer to the target integer
type through (size_t).

Also fix a comment and reformat the surrounding code.
This commit is contained in:
Cosmin Truta
2022-09-14 11:07:36 +03:00
parent 0c2388cdae
commit e9e9801a84
2 changed files with 18 additions and 20 deletions
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31
pngpriv.h
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@@ -556,14 +556,14 @@
#endif
/* These macros may need to be architecture dependent. */
#define PNG_ALIGN_NONE 0 /* do not use data alignment */
#define PNG_ALIGN_ALWAYS 1 /* assume unaligned accesses are OK */
#define PNG_ALIGN_NONE 0 /* do not use data alignment */
#define PNG_ALIGN_ALWAYS 1 /* assume unaligned accesses are OK */
#ifdef offsetof
# define PNG_ALIGN_OFFSET 2 /* use offsetof to determine alignment */
# define PNG_ALIGN_OFFSET 2 /* use offsetof to determine alignment */
#else
# define PNG_ALIGN_OFFSET -1 /* prevent the use of this */
#endif
#define PNG_ALIGN_SIZE 3 /* use sizeof to determine alignment */
#define PNG_ALIGN_SIZE 3 /* use sizeof to determine alignment */
#ifndef PNG_ALIGN_TYPE
/* Default to using aligned access optimizations and requiring alignment to a
@@ -577,26 +577,25 @@
/* This is used because in some compiler implementations non-aligned
* structure members are supported, so the offsetof approach below fails.
* Set PNG_ALIGN_SIZE=0 for compiler combinations where unaligned access
* is good for performance. Do not do this unless you have tested the result
* and understand it.
* is good for performance. Do not do this unless you have tested the
* result and understand it.
*/
# define png_alignof(type) (sizeof (type))
# define png_alignof(type) (sizeof(type))
#else
# if PNG_ALIGN_TYPE == PNG_ALIGN_OFFSET
# define png_alignof(type) offsetof(struct{char c; type t;}, t)
# define png_alignof(type) offsetof(struct{char c; type t;}, t)
# else
# if PNG_ALIGN_TYPE == PNG_ALIGN_ALWAYS
# define png_alignof(type) (1)
# endif
/* Else leave png_alignof undefined to prevent use thereof */
# if PNG_ALIGN_TYPE == PNG_ALIGN_ALWAYS
# define png_alignof(type) 1
# endif
/* Else leave png_alignof undefined to prevent use thereof */
# endif
#endif
/* This implicitly assumes alignment is always to a power of 2. */
/* This implicitly assumes alignment is always a multiple of 2. */
#ifdef png_alignof
# define png_isaligned(ptr, type)\
(((type)((const char*)ptr-(const char*)0) & \
(type)(png_alignof(type)-1)) == 0)
# define png_isaligned(ptr, type) \
(((type)(size_t)((const void*)(ptr)) & (type)(png_alignof(type)-1)) == 0)
#else
# define png_isaligned(ptr, type) 0
#endif