Commit fa2b6ea09253ce06152bc31591f6b84a3286502d
2024-01-12T18:21:41
Eliminate duplicate copies of jpeg_nbits_table ef9a4e05ba919494cbebe50e15f332de5ab97e82 (libjpeg-turbo 1.4.x), which was based on https://bug815473.bmoattachments.org/attachment.cgi?id=692126 (https://bugzilla.mozilla.org/show_bug.cgi?id=815473), modified the C baseline Huffman encoder so that it precomputes jpeg_nbits_table, in order to facilitate sharing the table among multiple processes. However, libjpeg-turbo never shared the table, and because the table was implemented as a static array, f3a8684cd1c28e557d394470962a7a224c76ddbc (libjpeg-turbo 1.5.x) and 37bae1a0e977ee1ba769e6f0aa27e519ab6e58c6 (libjpeg-turbo 2.0.x) each introduced a duplicate copy of the table for (respectively) the SSE2 baseline Huffman encoder and the C progressive Huffman encoder. This commit does the following: - Move the duplicated code in jchuff.c and jcphuff.c, originally introduced in 0cfc4c17b740cb2cbb11f9d85c8ab3745d5b913a and 37bae1a0e977ee1ba769e6f0aa27e519ab6e58c6, into a header (jpeg_nbits.h). - Credit the co-author of 0cfc4c17b740cb2cbb11f9d85c8ab3745d5b913a. (Refer to https://sourceforge.net/p/libjpeg-turbo/patches/57). - Modify the SSE2 baseline Huffman encoder so that the C Huffman encoders can share its definition of jpeg_nbits_table. - Move the definition of jpeg_nbits_table into a C source file (jpeg_nbits.c) rather than a header, and define the table only if USE_CLZ_INTRINSIC is undefined and the SSE2 baseline Huffman encoder will not be built. - Apply hidden symbol visibility to the shared definition of jpeg_nbits_table, if the compiler supports the necessary attribute. (In practice, only Visual C++ doesn't.) Closes #114 See also: https://bugzilla.mozilla.org/show_bug.cgi?id=1501523