[Tarantool-patches] [PATCH luajit 1/2] Fix tonumber("-0").

[sergos]

Hi!

Thanks for the patch, LGTM.

Sergos

> On 26 Jan 2022, at 15:19, Sergey Kaplun <skaplun at tarantool.org> wrote:
> 
> From: Mike Pall <mike>
> 
> Reported by bluecheetah001.
> 
> (cherry picked from 45a7e5073ce0a59465fef0b80bb08bd4e76b7979)
> 
> Common case for scanning a string containing a number is a string with a
> decimal number. For this case, a decimal number first casts to int32_t
> and later to double (lua_Number) if necessary. Information about sign of
> 0 is lost during the cast to int32_t. So resulting TValue contains `0.`
> instead of `-0.`.
> 
> This patch removes cast to int32_t for the case when resulting TValue
> contains double value.
> 
> Sergey Kaplun:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#6548
> ---
> src/lj_strscan.c                              |  5 ++---
> .../lj-528-tonumber-0.test.lua                | 19 +++++++++++++++++++
> 2 files changed, 21 insertions(+), 3 deletions(-)
> create mode 100644 test/tarantool-tests/lj-528-tonumber-0.test.lua
> 
> diff --git a/src/lj_strscan.c b/src/lj_strscan.c
> index 08f41f19..4e4ef6d3 100644
> --- a/src/lj_strscan.c
> +++ b/src/lj_strscan.c
> @@ -495,12 +495,11 @@ StrScanFmt lj_strscan_scan(const uint8_t *p, MSize len, TValue *o,
>     /* Fast path for decimal 32 bit integers. */
>     if (fmt == STRSCAN_INT && base == 10 &&
> 	(dig < 10 || (dig == 10 && *sp <= '2' && x < 0x80000000u+neg))) {
> -      int32_t y = neg ? -(int32_t)x : (int32_t)x;
>       if ((opt & STRSCAN_OPT_TONUM)) {
> -	o->n = (double)y;
> +	o->n = neg ? -(double)x : (double)x;
> 	return STRSCAN_NUM;
>       } else {
> -	o->i = y;
> +	o->i = neg ? -(int32_t)x : (int32_t)x;
> 	return STRSCAN_INT;
>       }
>     }
> diff --git a/test/tarantool-tests/lj-528-tonumber-0.test.lua b/test/tarantool-tests/lj-528-tonumber-0.test.lua
> new file mode 100644
> index 00000000..03ba2aff
> --- /dev/null
> +++ b/test/tarantool-tests/lj-528-tonumber-0.test.lua
> @@ -0,0 +1,19 @@
> +local tap = require('tap')
> +
> +-- Test disabled for DUALNUM mode default for some arches.
> +-- See also https://github.com/LuaJIT/LuaJIT/pull/787.
> +require("utils").skipcond(
> +  jit.arch ~= "x86" and jit.arch ~= "x64",
> +  jit.arch.." in DUALNUM mode is clumsy for now"
> +)
> +
> +-- Test file to demonstrate LuaJIT `tonumber('-0')` incorrect
> +-- behaviour.
> +-- See also https://github.com/LuaJIT/LuaJIT/issues/528.
> +local test = tap.test('lj-528-tonumber-0')
> +test:plan(1)
> +
> +-- As numbers `-0 == 0`, so convert it back to string.
> +test:ok(tostring(tonumber('-0')) == '-0', 'correct "-0" string parsing')
> +
> +os.exit(test:check() and 0 or 1)
> -- 
> 2.34.1
>