37 lines
781 B
Lua
37 lines
781 B
Lua
local bit = {}
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local LUA_NBITS = 32
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local ALLONES = (~(((~0) << (LUA_NBITS - 1)) << 1))
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local function trim(x)
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return (x & ALLONES)
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end
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local function mask(n)
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return (~((ALLONES << 1) << ((n) - 1)))
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end
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local function check_args(field, width)
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assert(field >= 0, "field cannot be negative")
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assert(width > 0, "width must be positive")
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assert(field + width < LUA_NBITS and field + width >= 0,
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"trying to access non-existent bits")
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end
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function bit.extract(n, field, width)
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local w = width or 1
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check_args(field, w)
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local m = trim(n)
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return m >> field & mask(w)
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end
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function bit.replace(n, v, field, width)
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local w = width or 1
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check_args(field, w)
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local m = trim(n)
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local x = v & mask(width);
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return m & ~(mask(w) << field) | (x << field)
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end
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return bit
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