Introduce std.mem.readPackedInt and improve bitcasting of packed memory layouts#13221
Introduce std.mem.readPackedInt and improve bitcasting of packed memory layouts#13221andrewrk merged 5 commits intoziglang:masterfrom
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std.mem.readPackedInt and improve bitcasting of packed memory layouts.std.mem.readPackedInt and improve bitcasting of packed memory layouts
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Very dense math stuff. I wonder, what the perf results will be.
So far writePackedIntLittle and writePackedIntBig have no test coverage testing them against another and it would be nice to reverse the ints with byteswap to ensure both work as expected. At least, if that is feasible.
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I think this is already covered. |
| random.int(BackingType), // random | ||
| }) |init_value| { | ||
| const uTs = [_]type{ u1, u3, u7, u8, u9, u10, u15, u16, u86 }; | ||
| const iTs = [_]type{ i1, i3, i7, i8, i9, i10, i15, i16, i86 }; |
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Brief call-out: The codegen on this test is absurd.
Parts of this inline for are generated 18 * 4 * 3 = 216 times. It was vital while developing, but we may want to disable it or pare down the tested combinations now that we know these functions work.
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This looks like an important changeset. The first thing I started looking at is the changed behavior tests, and I noticed that it links to a closed issue. So I'm guessing that this PR needs to be revisited before it is ready for review-
These utility functions allow reading from (stage2) packed memory at runtime-known offsets.
Packed memory has a well-defined layout that doesn't require conversion from an integer to read from. Let's use it :-) This change means that for bitcasting to/from a packed value that is N layers deep, we no longer have to create N temporary big-ints and perform N copies. Other miscellaneous improvements: - Adds support for casting to packed enums and vectors - Fixes bitcasting to/from vectors outside of a packed struct - Adds a fast path for bitcasting <= u/i64 - Fixes bug when bitcasting f80 which would clear following fields This also changes the bitcast memory layout of exotic integers on big-endian systems to match what's empirically observed on our targets. Technically, this layout is not guaranteed by LLVM so we should probably ban bitcasts that reveal these padding bits, but for now this is an improvement.
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Packed memory has a well-defined layout that doesn't require actually using a BigInt to read from. Let's use it :-)
Included changes:
readPackedInt,writePackedIntand friends tostd.mem