Re: [Tarantool-patches] [PATCH luajit 1/2] Fix bit op coercion in DUALNUM builds.

[Sergey Bronnikov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

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Hello, Sergey,

thanks for the patch! LGTM

On 02.10.2024 11:09, Sergey Kaplun wrote:
> From: Mike Pall <mike>
>
> Thanks to Sergey Kaplun.
>
> (cherry picked from commit f5fd22203eadf57ccbaa4a298010d23974b22fc0)
>
> The `lj_carith_check64()` function coerces the given number value to the
> 32-bit wide value. In this case, the 64-bit-wide operands will lose
> upper bits.
>
> This patch removes the excess coercion for the DUALNUM mode.
>
> Sergey Kaplun:
> * added the description and the test for the problem
>
> Part of tarantool/tarantool#10199
> ---
>   src/lj_carith.c                               |  4 +---
>   .../lj-1273-dualnum-bit-coercion.test.lua     | 19 +++++++++++++++++++
>   2 files changed, 20 insertions(+), 3 deletions(-)
>   create mode 100644 test/tarantool-tests/lj-1273-dualnum-bit-coercion.test.lua
>
> diff --git a/src/lj_carith.c b/src/lj_carith.c
> index 90b3220f..eb56d552 100644
> --- a/src/lj_carith.c
> +++ b/src/lj_carith.c
> @@ -349,9 +349,7 @@ uint64_t lj_carith_check64(lua_State *L, int narg, CTypeID *id)
>     if (LJ_LIKELY(tvisint(o))) {
>       return (uint32_t)intV(o);
>     } else {
> -    int32_t i = lj_num2bit(numV(o));
> -    if (LJ_DUALNUM) setintV(o, i);
> -    return (uint32_t)i;
> +    return (uint32_t)lj_num2bit(numV(o));
>     }
>   }
>   
> diff --git a/test/tarantool-tests/lj-1273-dualnum-bit-coercion.test.lua b/test/tarantool-tests/lj-1273-dualnum-bit-coercion.test.lua
> new file mode 100644
> index 00000000..e83dbbcd
> --- /dev/null
> +++ b/test/tarantool-tests/lj-1273-dualnum-bit-coercion.test.lua
> @@ -0,0 +1,19 @@
> +local tap = require('tap')
> +
> +-- Test file to demonstrate LuaJIT misbehaviour on operating
> +-- for 64-bit operands in built-in `bit` library in DUALNUM mode.
> +-- See also,https://github.com/LuaJIT/LuaJIT/issues/1273.
> +
> +local test = tap.test('lj-1273-dualnum-bit-coercion')
> +test:plan(1)
> +
> +local bit = require('bit')
> +
> +-- The cdata value for 2 ^ 33.
> +local EXPECTED = 2 ^ 33 + 0LL
> +-- Same value is used as mask for `bit.band()`.
> +local MASK = EXPECTED
> +
> +test:is(bit.band(2 ^ 33, MASK), EXPECTED, 'correct bit.band result')
> +
> +test:done(true)

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