128 lines
2.7 KiB
Lua
Executable File
128 lines
2.7 KiB
Lua
Executable File
-- write formats
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-- return true if they have consumed a value from the input stream
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-- return false/nil otherwise (ie, the next value will be preserved
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-- for subsequent calls, eg skip/pad)
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-- Copyright © 2008 Ben "ToxicFrog" Kelly; see COPYING
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local require,error,setmetatable,string,print,math,unpack,io
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= require,error,setmetatable,string,print,math,unpack,io
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module((...))
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local struct = require (_PACKAGE:sub(1,-2))
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local common = require (_PACKAGE.."common")
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local fp = require (_PACKAGE.."fp")
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local pack = setmetatable({}, { __index = common })
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-- boolean
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function pack.b(fd, d, w)
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return pack.u(fd, (d and 1) or 0, w)
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end
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-- counted string
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-- a string immediately prefaced with its length as a uint
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function pack.c(fd, d, w)
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pack.u(fd, #d, w)
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return pack.s(fd, d)
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end
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-- floating point
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function pack.f(fd, d, w)
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if not fp.w[w] then
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error("struct.pack: illegal floating point width")
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end
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-- local f = fp.w[w](d)
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-- print(f, type(f))
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return pack.s(fd, fp.w[w](d), w)
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end
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-- signed int
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function pack.i(fd, d, w)
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if d < 0 then
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d = 2^(w*8) + d
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end
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return pack.u(fd, d, w)
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end
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-- bitmask
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-- we use a string here because using an unsigned will lose data on bitmasks
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-- wider than lua's native number format
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function pack.m(fd, d, w)
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local buf = ""
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for i=1,w*8,8 do
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local bits = { unpack(d, i, i+7) }
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local byte = string.char(struct.implode(bits, 8))
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if pack.is_bigendian then
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buf = byte..buf
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else
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buf = buf..byte
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end
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end
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return pack.s(fd, buf, w)
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end
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-- fixed point bit aligned
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function pack.P(fd, d, dp, fp)
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if (dp+fp) % 8 ~= 0 then
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error "total width of fixed point value must be byte multiple"
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end
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return pack.i(fd, d * 2^fp, (dp+fp)/8)
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end
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-- fixed point byte aligned
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function pack.p(fd, d, dp, fp)
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return pack.P(fd, d, dp*8, fp*8)
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end
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-- fixed length string
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-- length 0 is write string as is
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-- length >0 is write exactly w bytes, truncating or padding as needed
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function pack.s(fd, d, w)
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w = w or #d
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if w == 0 then return end
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if #d < w then
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d = d..string.char(0):rep(w-#d)
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end
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return fd:write(d:sub(1,w))
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end
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-- unsigned int
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function pack.u(fd, d, w)
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local s = ""
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for i=1,w do
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if pack.is_bigendian then
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s = string.char(d % 2^8) .. s
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else
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s = s .. string.char(d % 2^8)
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end
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d = math.trunc(d/2^8)
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end
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return pack.s(fd, s, w)
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end
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-- skip/pad
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-- this is technically a control format, so it has a different signature
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-- specifically, there is no "data" argument
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function pack.x(fd, w)
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return pack.s(fd, "", w)
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end
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-- null terminated string
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-- w==nil is write string as is + termination
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-- w>0 is write exactly w bytes, truncating/padding and terminating
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function pack.z(fd, d, w)
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w = w or #d+1
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if #d >= w then
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d = d:sub(1, w-1)
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end
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return pack.s(fd, d.."\0", w)
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end
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return pack
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