179 lines
4.7 KiB
Forth
179 lines
4.7 KiB
Forth
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# Helpers for Unicode "code points".
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# https://en.wikipedia.org/wiki/Code_point
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#
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# Mu has no characters, only code points and graphemes.
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# Code points are the indivisible atoms of text streams.
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# Graphemes are the smallest self-contained unit of text.
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# Graphemes may consist of multiple code points.
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#
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# Mu graphemes are always represented in utf-8, and they are required to fit
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# in 4 bytes.
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#
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# Mu doesn't currently support combining code points, or graphemes made of
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# multiple code points.
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# transliterated from tb_utf8_unicode_to_char in https://github.com/nsf/termbox
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# https://wiki.tcl-lang.org/page/UTF%2D8+bit+by+bit explains the algorithm
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fn to-grapheme in: code-point -> out/eax: grapheme {
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$to-grapheme:body: {
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var c/eax: int <- copy in
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var num-trailers/ecx: int <- copy 0
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var first/edx: int <- copy 0
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$to-grapheme:compute-length: {
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# single byte: just return it
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compare c, 0x7f
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{
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break-if->
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out <- copy c
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break $to-grapheme:body
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}
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# 2 bytes
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compare c, 0x7ff
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{
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break-if->
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num-trailers <- copy 1
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first <- copy 0xc0
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break $to-grapheme:compute-length
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}
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# 3 bytes
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compare c, 0xffff
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{
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break-if->
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num-trailers <- copy 2
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first <- copy 0xe0
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break $to-grapheme:compute-length
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}
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# 4 bytes
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compare c, 0x1fffff
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{
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break-if->
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num-trailers <- copy 3
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first <- copy 0xf0
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break $to-grapheme:compute-length
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}
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# more than 4 bytes: unsupported
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compare c, 0x1fffff
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{
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break-if->
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print-string-to-real-screen "unsupported code point "
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print-int32-hex-to-real-screen c
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print-string-to-real-screen "\n"
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var exit-status/ebx: int <- copy 1
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syscall_exit
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}
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}
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# emit trailer bytes, 6 bits from 'in', first two bits '10'
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var byte-shifts/ebx: int <- copy 0
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var result/edi: int <- copy 0
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{
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compare num-trailers, 0
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break-if-<=
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var tmp/esi: int <- copy c
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tmp <- and 0x3f
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tmp <- or 0x80
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tmp <- shift-left-bytes tmp, byte-shifts
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result <- or tmp
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# update loop state
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c <- shift-right 6
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byte-shifts <- increment
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num-trailers <- decrement
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loop
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}
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# emit engine
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var tmp/esi: int <- copy c
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tmp <- or first
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tmp <- shift-left-bytes tmp, byte-shifts
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result <- or tmp
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#
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out <- copy result
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}
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}
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# single-byte code point have identical graphemes
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fn test-to-grapheme-single-byte {
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var in-int/ecx: int <- copy 0
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{
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compare in-int, 0x7f
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break-if->
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var in/eax: code-point <- copy in-int
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var out/eax: grapheme <- to-grapheme in
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var out-int/eax: int <- copy out
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check-ints-equal out-int, in-int, "F - test-to-grapheme-single-byte"
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in-int <- increment
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loop
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}
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}
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# smallest 2-byte utf-8
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fn test-to-grapheme-two-bytes-min {
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var in/eax: code-point <- copy 0x80 # 10 000000
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var out/eax: grapheme <- to-grapheme in
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var out-int/eax: int <- copy out
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check-ints-equal out-int, 0xc280, "F 2gr" # 110 00010 10 000000
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}
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# largest 2-byte utf-8
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fn test-to-grapheme-two-bytes-max {
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var in/eax: code-point <- copy 0x7ff # 11111 111111
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var out/eax: grapheme <- to-grapheme in
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var out-int/eax: int <- copy out
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check-ints-equal out-int, 0xdfbf, "F 2gr" # 110 11111 10 111111
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}
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# smallest 3-byte utf-8
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fn test-to-grapheme-three-bytes-min {
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var in/eax: code-point <- copy 0x800 # 100000 000000
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var out/eax: grapheme <- to-grapheme in
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var out-int/eax: int <- copy out
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check-ints-equal out-int, 0xc280, "F 2gr" # 1110 0000 10 100000 10 000000
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}
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# needed because available primitives only shift by a literal/constant number of bits
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fn shift-left-bytes n: int, k: int -> result/esi: int {
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var i/eax: int <- copy 0
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result <- copy n
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{
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compare i, k
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break-if->=
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compare i, 4 # only 4 bytes in 32 bits
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break-if->=
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result <- shift-left 8
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i <- increment
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loop
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}
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}
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fn test-shift-left-bytes-0 {
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var result/esi: int <- shift-left-bytes 1, 0
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check-ints-equal result, 1, "F - shift-left-bytes 0"
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}
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fn test-shift-left-bytes-1 {
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var result/esi: int <- shift-left-bytes 1, 1
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check-ints-equal result, 0x100, "F - shift-left-bytes 1"
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}
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fn test-shift-left-bytes-2 {
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var result/esi: int <- shift-left-bytes 1, 2
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check-ints-equal result, 0x10000, "F - shift-left-bytes 2"
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}
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fn test-shift-left-bytes-3 {
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var result/esi: int <- shift-left-bytes 1, 3
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check-ints-equal result, 0x1000000, "F - shift-left-bytes 3"
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}
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fn test-shift-left-bytes-4 {
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var result/esi: int <- shift-left-bytes 1, 4
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check-ints-equal result, 0, "F - shift-left-bytes 4"
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}
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fn test-shift-left-bytes-5 {
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var result/esi: int <- shift-left-bytes 1, 5
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check-ints-equal result, 0, "F - shift-left-bytes >4"
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}
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#? fn main {
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#? run-tests
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#? }
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