[ARROW-7404] [C++][Gandiva] Fix utf8 char length error on Arm64

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.16.0
• Component/s: C++ - Gandiva
• Labels: pull-request-available
• Flags: Patch
• External issue URL: https://github.com/apache/arrow/issues/23678
• Assignee: Yibo Cai
• Reporter: Yibo Cai
• Created: 17/Dec/19 02:21
• Updated: 11/Jan/23 07:53
• Resolved: 17/Dec/19 04:33

Description

Current code checks if a UTF-8 eight-bit code unit is within 0x00~0x7F
by "if (c >= 0)", where c is defined as "char". This checking assumes
char is always signed, which is not true[1]. On Arm64, char is unsigned
by default and causes some Gandiva unit tests fail.

Fix it by casting to "signed char" explicitly.

[1] Cited from https://en.cppreference.com/w/cpp/language/types
The signedness of char depends on the compiler and the target platform:
the defaults for ARM and PowerPC are typically unsigned, the defaults
for x86 and x64 are typically signed.

Issue Links

• links to: GitHub Pull Request #6043