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# Helpers for Unicode.
#
# Mu has no characters, only code points and graphemes.
# Code points are the indivisible atoms of text streams.
# https://en.wikipedia.org/wiki/Code_point
# Graphemes are the smallest self-contained unit of text.
# Graphemes may consist of multiple code points.
#
# Mu graphemes are always represented in utf-8, and they are required to fit
# in 4 bytes.
#
# Mu doesn't currently support combining code points, or graphemes made of
# multiple code points. One day we will.
# We also don't currently support code points that translate into multiple
# or wide graphemes. (In particular, Tab will never be supported.)
# transliterated from tb_utf8_unicode_to_char in https://github.com/nsf/termbox
# https://wiki.tcl-lang.org/page/UTF%2D8+bit+by+bit explains the algorithm
#
# The day we want to support combining characters, this function will need to
# take multiple code points. Or something.
fn to-grapheme in: code-point -> _/eax: grapheme {
var c/eax: int <- copy in
var num-trailers/ecx: int <- copy 0
var first/edx: int <- copy 0
$to-grapheme:compute-length: {
# single byte: just return it
compare c, 0x7f
{
break-if->
var g/eax: grapheme <- copy c
return g
}
# 2 bytes
compare c, 0x7ff
{
break-if->
num-trailers <- copy 1
first <- copy 0xc0
break $to-grapheme:compute-length
}
# 3 bytes
compare c, 0xffff
{
break-if->
num-trailers <- copy 2
first <- copy 0xe0
break $to-grapheme:compute-length
}
# 4 bytes
compare c, 0x1fffff
{
break-if->
num-trailers <- copy 3
first <- copy 0xf0
break $to-grapheme:compute-length
}
# more than 4 bytes: unsupported
# TODO: print error message to stderr
compare c, 0x1fffff
{
break-if->
return 0
}
}
# emit trailer bytes, 6 bits from 'in', first two bits '10'
var result/edi: grapheme <- copy 0
{
compare num-trailers, 0
break-if-<=
var tmp/esi: int <- copy c
tmp <- and 0x3f
tmp <- or 0x80
result <- shift-left 8
result <- or tmp
# update loop state
c <- shift-right 6
num-trailers <- decrement
loop
}
# emit engine
result <- shift-left 8
result <- or c
result <- or first
#
return result
}
# TODO: bring in tests once we have check-ints-equal
# read the next grapheme from a stream of bytes
fn read-grapheme in: (addr stream byte) -> _/eax: grapheme {
# if at eof, return EOF
{
var eof?/eax: boolean <- stream-empty? in
compare eof?, 0 # false
break-if-=
return 0xffffffff
}
var c/eax: byte <- read-byte in
var num-trailers/ecx: int <- copy 0
$read-grapheme:compute-length: {
# single byte: just return it
compare c, 0xc0
{
break-if->=
var g/eax: grapheme <- copy c
return g
}
compare c, 0xfe
{
break-if-<
var g/eax: grapheme <- copy c
return g
}
# 2 bytes
compare c, 0xe0
{
break-if->=
num-trailers <- copy 1
break $read-grapheme:compute-length
}
# 3 bytes
compare c, 0xf0
{
break-if->=
num-trailers <- copy 2
break $read-grapheme:compute-length
}
# 4 bytes
compare c, 0xf8
{
break-if->=
num-trailers <- copy 3
break $read-grapheme:compute-length
}
# TODO: print error message
return 0
}
# prepend trailer bytes
var result/edi: grapheme <- copy c
var num-byte-shifts/edx: int <- copy 1
{
compare num-trailers, 0
break-if-<=
var tmp/eax: byte <- read-byte in
var tmp2/eax: int <- copy tmp
tmp2 <- shift-left-bytes tmp2, num-byte-shifts
result <- or tmp2
# update loop state
num-byte-shifts <- increment
num-trailers <- decrement
loop
}
return result
}
# needed because available primitives only shift by a literal/constant number of bits
fn shift-left-bytes n: int, k: int -> _/eax: int {
var i/ecx: int <- copy 0
var result/eax: int <- copy n
{
compare i, k
break-if->=
compare i, 4 # only 4 bytes in 32 bits
break-if->=
result <- shift-left 8
i <- increment
loop
}
return result
}
# write a grapheme to a stream of bytes
# this is like write-to-stream, except we skip leading 0 bytes
fn write-grapheme out: (addr stream byte), g: grapheme {
$write-grapheme:body: {
var c/eax: int <- copy g
append-byte out, c # first byte is always written
c <- shift-right 8
compare c, 0
break-if-= $write-grapheme:body
append-byte out, c
c <- shift-right 8
compare c, 0
break-if-= $write-grapheme:body
append-byte out, c
c <- shift-right 8
compare c, 0
break-if-= $write-grapheme:body
append-byte out, c
}
}
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