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kc3-lang/libxkbcommon/src/xkbcomp

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  • Author : Wismill
    Date : 2023-05-01 22:30:41
    Hash : 5b5b67f2
    Message : Add support for modmap None (#291) Unlike current xkbcommon, X11’s xkbcomp allows to remove entries in the modifiers’ map using “modifier_map None { … }”. “None” is translated to the special value “XkbNoModifier” defined in “X11/extensions/XKB.h”. Then it relies on the fact that in "CopyModMapDef", the following code: 1U << entry->modifier ends up being zero when “entry->modifier” is “XkbNoModifier” (i.e. 0xFF). Indeed, it relies on the overflow behaviour of the left shift, which in practice resolves to use only the 5 low bits of the shift amount, i.e. 0x1F here. Then the result of “1U << 0xFF” is cast to “char”, i.e. 0. This is a good trick but too magical, so in libxkbcommon we will use an explicit test against our new constant XKB_MOD_NONE.