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jconfig.h: Restore BITS_IN_JSAMPLE macro

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Because of e8b40f3c2b, we now support
multiple data precisions in the same libjpeg API library, so
BITS_IN_JSAMPLE is no longer used to specify the data precision at build
time.  However, some downstream software expects the macro to be
defined.  Since 12-bit data precision is an opt-in feature that requires
explicitly calling 12-bit-specific libjpeg API functions and using
12-bit-specific data types, the unmodified portion of the libjpeg API
still behaves as if it were built for 8-bit precision, and JSAMPLE is
still literally an 8-bit data type.  Thus, it is correct to externally
define BITS_IN_JSAMPLE to 8 in jconfig.h.  Since the build system also
uses BITS_IN_JSAMPLE internally to build both 8-bit and 12-bit versions
of relevant modules, the definition of BITS_IN_JSAMPLE in jconfig.h is
now guarded by #ifndef BITS_IN_JSAMPLE.  (Hopefully that doesn't cause
any problems.)

Fixes #632
This commit is contained in:
DRC
2022-11-23 16:26:42 -06:00
parent 4afa4d3ee8
commit 8b9bc4b963
1 changed files with 13 additions and 0 deletions
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13
jconfig.h.in
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@@ -21,6 +21,19 @@
/* Use accelerated SIMD routines when using 8-bit samples */
#cmakedefine WITH_SIMD 1
/* This version of libjpeg-turbo supports run-time selection of data precision,
* so BITS_IN_JSAMPLE is no longer used to specify the data precision at build
* time. However, some downstream software expects the macro to be defined.
* Since 12-bit data precision is an opt-in feature that requires explicitly
* calling 12-bit-specific libjpeg API functions and using 12-bit-specific data
* types, the unmodified portion of the libjpeg API still behaves as if it were
* built for 8-bit precision, and JSAMPLE is still literally an 8-bit data
* type. Thus, it is correct to define BITS_IN_JSAMPLE to 8 here.
*/
#ifndef BITS_IN_JSAMPLE
#define BITS_IN_JSAMPLE 8
#endif
#ifdef _WIN32
#undef RIGHT_SHIFT_IS_UNSIGNED