As per the const correctness rules, top-level const-ness of data
in automatic scopes does not propagate outside of these scopes
(unlike const-ness at lower levels, such as pointers to const data).
Previously, const was used liberally, but inconsistently across the
libpng codebase. Using const wherever applicable is not incorrect.
However, _consistent_ use of const is difficult to maintain in such
conditions.
In conclusion, we shall continue to use const only where doing so is
strictly necessary:
1. If a function guarantees that it will not modify an argument
passed by pointer, the corresponding function parameter should be
a pointer-to-const (const T *).
2. Static data should not be modified, therefore it should be const.
Reference:
Google C++ Style Guide
https://google.github.io/styleguide/cppguide.html#Use_of_const
In v1.6.0, compiler support for const became a requirement.
It should be used consistently. To maintain backwards compatibility,
PNG_CONST is still maintained in deprecated form.
In v1.6.0, size_t became a required type. It should be used
consistently. To maintain backwards compatibility, png_size_t
is still maintained in deprecated form.
result when integers appear on both sides of a compare. Worked around the
others by forcing the strict-overflow setting in the relevant functions to
a level where they are not reported.
Changed "FALL THROUGH" comments to "FALLTHROUGH" because GCC doesn't like
the space.
Worked around some C-style casts from (void*) because g++ 5.4.0 objects
to them.
Increased the buffer size for 'sprint' to pass the gcc 7.1.0 'sprint
overflow' check that is on by default with -Wall -Wextra.
As suggested in the comments gamma values outside the range currently permitted
by png_set_alpha_mode are useful for HDR data encoding. These values are
already permitted by png_set_gamma so it is reasonable caution to extend the
png_set_alpha_mode range as HDR imaging systems are starting to emerge.
Signed-off-by: John Bowler <jbowler@acm.org>
The old code incorrectly calculated the output rowbytes when the
application decreased either the number of channels or the bit depth (or
both) in a user transform. This was safe; libpng overallocated buffer
space (potentially by quite a lot; up to 4 times the amount required)
but, from 1.5.4 on, resulted in a png_error.
Signed-off-by: John Bowler <jbowler@acm.org>
input that was made in version 1.6.17beta01, to preserve legacy
behavior even though it was incorrect. Instead, added new API
png_set_filter_16() and png_set_add_alpha_16() that set a flag to
make png_do_read_filter() interpret the filler bytes properly.
