compress: Elide long-offset path on 64-bit - #4772
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ZSTD_seqToCodes() only enables longOffsets on 32-bit builds because the 64-bit bitstream accumulator can hold every supported offset. However, ZSTD_encodeSequences_body() still tests the runtime flag for the first sequence and every sequence in its hot loop. Make the architecture condition explicit at both branches so 64-bit compilers can discard the unreachable path. Add an assertion documenting the invariant while preserving the existing 32-bit behavior. In five alternating GCC 11.5 fullbench runs encoding sequences for an 8 MiB, 50%-compressible level-3 sample, throughput increased from 1201.6 to 1213.4 MB/s on average (+1.0%) with identical 2,706,887-byte output. The fullbench text section also shrank by 512 bytes. Signed-off-by: Usama Arif <usama.arif@linux.dev>
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ZSTD_seqToCodes() only enables longOffsets on 32-bit builds because the 64-bit bitstream accumulator can hold every supported offset. However, ZSTD_encodeSequences_body() still tests the runtime flag for the first sequence and every sequence in its hot loop.
Make the architecture condition explicit at both branches so 64-bit compilers can discard the unreachable path. Add an assertion documenting the invariant while preserving the existing 32-bit behavior.
In five alternating GCC 11.5 fullbench runs encoding sequences for an 8 MiB, 50%-compressible level-3 sample, throughput increased from 1201.6 to 1213.4 MB/s on average (+1.0%) with identical 2,706,887-byte output. The fullbench text section also shrank by 512 bytes.