Adds two new getters to int for bit-counting: trailingZeroBitCount
(ctz) and oneBitCount (popcount). On native platforms they operate
on the full 64-bit two's-complement representation; on the web they
operate on the least-significant 32 bits.
Implementations:
- VM: unified C++ natives Integer_trailingZeroBitCount /
Integer_oneBitCount on _IntegerImplementation, using
Utils::CountTrailingZeros64 and Utils::CountOneBits64. The receiver
may be _Smi or _Mint at runtime.
- dart2js / DDC: clz32-based ctz and a SWAR popcount.
- dart2wasm: inlined i64.ctz and i64.popcnt intrinsics.
leadingZeroBitCount (clz) is intentionally excluded from this CL: its
result depends on the platform integer width (e.g. 1.leadingZeroBitCount
is 31 on web, 63 on native), and the same value can be derived from
the existing bitLength getter when needed.
Asm intrinsification on native architectures is intentionally left for
a separate follow-up CL.
Work towards https://github.com/dart-lang/sdk/issues/6486 (this CL
covers popcount and ctz from the bit-twiddling list; clz, rotate,
reverse, and others remain).
Work towards https://github.com/dart-lang/sdk/issues/1053 (efficient
BitSet implementation).
Bug: https://github.com/dart-lang/sdk/issues/52673
Bug: https://github.com/dart-lang/sdk/issues/38346
TEST=tests/corelib/int_bit_count_test
Change-Id: I8a5cdb5c91360478f47bbd6b9c84ca1c477aa8c7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/498041
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Auto-Submit: Modestas Valauskas <valauskasmodestas@gmail.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>
Modestas Valauskas
754239b077