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implement Btos;
# encoding details
# (Traditional) Shift-JIS
#
# 00..1f control characters
# 20 space
# 21..7f JIS X 0201:1976/1997 roman (see notes)
# 80 undefined
# 81..9f lead byte of JIS X 0208-1983 or JIS X 0202:1990/1997
# a0 undefined
# a1..df JIS X 0201:1976/1997 katakana
# e0..ea lead byte of JIS X 0208-1983 or JIS X 0202:1990/1997
# eb..ff undefined
#
# CP932 (windows-31J)
#
# this encoding scheme extends Shift-JIS in the following way
#
# eb..ec undefined (marked as lead bytes - see notes below)
# ed..ee lead byte of NEC-selected IBM extended characters
# ef undefined (marked as lead byte - see notes below)
# f0..f9 lead byte of User defined GAIJI (see note below)
# fa..fc lead byte of IBM extended characters
# fd..ff undefined
#
#
# Notes
#
# JISX 0201:1976/1997 roman
# this is the same as ASCII but with 0x5c (ASCII code for '\')
# representing the Yen currency symbol '¥' (U+00a5)
# This mapping is contentious, some conversion packages implent it
# others do not.
# The mapping files from The Unicode Consortium show cp932 mapping
# plain ascii in the range 00..7f whereas shift-jis maps 16r5c ('\') to the yen
# symbol (¥) and 16r7e ('~') to overline (¯)
#
# CP932 double-byte character codes:
#
# eb-ec, ef, f0-f9:
# Marked as DBCS LEAD BYTEs in the unicode mapping data
# obtained from:
# https://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP932.TXT
#
# but there are no defined mappings for codes in this range.
# It is not clear whether or not an implementation should
# consume one or two bytes before emitting an error char.
#
include "sys.m";
include "convcs.m";
sys : Sys;
MAXINT : con 16r7fffffff;
BADCHAR : con 16rFFFD;
KANAPAGES : con 1;
KANAPAGESZ : con 63;
KANACHAR0 : con 16ra1;
CP932PAGES : con 45; # 81..84, 87..9f, e0..ea, ed..ee, fa..fc
CP932PAGESZ : con 189; # 40..fc (including 7f)
CP932CHAR0 : con 16r40;
shiftjis := 0;
page0 := array [256] of { * => BADCHAR };
cp932 : string;
dbcsoff := array [256] of { * => -1 };
init(arg : string) : string
{
sys = load Sys Sys->PATH;
shiftjis = arg == "shiftjis";
(error, kana) := getmap("/lib/convcs/jisx0201kana", KANAPAGESZ, KANAPAGES);
if (error != nil)
return error;
(error, cp932) = getmap("/lib/convcs/cp932", CP932PAGESZ, CP932PAGES);
if (error != nil)
return error;
# jisx0201kana is mapped into 16rA1..16rDF
for (i := 0; i < KANAPAGESZ; i++)
page0[i + KANACHAR0] = kana[i];
# 00..7f same as ascii in cp932
for (i = 0; i <= 16r7f; i++)
page0[i] = i;
if (shiftjis) {
# shift-jis uses JIS X 0201 for the ASCII range
# this is the same as ASCII apart from
# 16r5c ('\') maps to yen symbol (¥) and 16r7e ('~') maps to overline (¯)
page0['\\'] = '¥';
page0['~'] = '¯';
}
# pre-calculate DBCS page numbers to mapping file page numbers
# and mark codes in page0 that are DBCS lead bytes
pnum := 0;
for (i = 16r81; i <= 16r84; i++){
page0[i] = -1;
dbcsoff[i] = pnum++;
}
for (i = 16r87; i <= 16r9f; i++){
page0[i] = -1;
dbcsoff[i] = pnum++;
}
for (i = 16re0; i <= 16rea; i++) {
page0[i] = -1;
dbcsoff[i] = pnum++;
}
if (!shiftjis) {
# add in cp932 extensions
for (i = 16red; i <= 16ree; i++) {
page0[i] = -1;
dbcsoff[i] = pnum++;
}
for (i = 16rfa; i <= 16rfc; i++) {
page0[i] = -1;
dbcsoff[i] = pnum++;
}
}
return nil;
}
btos(nil : Convcs->State, b : array of byte, n : int) : (Convcs->State, string, int)
{
nbytes := 0;
str := "";
if (n == -1)
n = MAXINT;
for (i := 0; i < len b && len str < n; i++) {
b1 := int b[i];
ch := page0[b1];
if (ch != -1) {
str[len str] = ch;
nbytes++;
continue;
}
# DBCS
i++;
if (i >= len b)
break;
pnum := dbcsoff[b1];
ix := (int b[i]) - CP932CHAR0;
if (pnum == -1 || ix < 0 || ix >= CP932PAGESZ)
str[len str] = BADCHAR;
else
str[len str] = cp932[(pnum * CP932PAGESZ)+ix];
nbytes += 2;
}
return (nil, str, nbytes);
}
getmap(path : string, pgsz, npgs : int) : (string, string)
{
fd := sys->open(path, Sys->OREAD);
if (fd == nil)
return (sys->sprint("%s: %r", path), nil);
buf := array[(pgsz * npgs) * Sys->UTFmax] of byte;
nread := 0;
for (;nread < len buf;) {
n := sys->read(fd, buf[nread:], Sys->ATOMICIO);
if (n <= 0)
break;
nread += n;
}
map := string buf[:nread];
if (len map != (pgsz * npgs))
return (sys->sprint("%s: bad data", path), nil);
return (nil, map);
}
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