[PATCH v3] Implement graphemewidth

["S. Gilles" <sgilles@xxxxxxxxxxxx>]

---
Since v2:

 - I'd somehow got it into my head that the arrays in chartype.myr
   were inversion lists. This, of course, isn't true. Therefore,
   drop the duplicate binary search and just use findc.

As a side note, I have no idea how to tell git "Please treat
lib/std/test/utf.myr as a UTF-8 text file and don't do that binary
thing". I thought --no-binary would do it, but it omits the file
entirely. The functionality should be there, since
lib/std/test/chartype.myr is handled sanely, but I don't know how
to force it.  It's just a couple tests for std.strcellwidth() to
check that I used strstep correctly.
---
 lib/std/chartype.myr      | 470 ++++++++++++++++++++++++++++++++++++++++++++++
 lib/std/fmt.myr           |  10 +-
 lib/std/test/chartype.myr |  18 ++
 lib/std/test/fmt.myr      |   4 +
 lib/std/test/utf.myr      | Bin 0 -> 1305 bytes
 lib/std/utf.myr           |  29 +++
 6 files changed, 522 insertions(+), 9 deletions(-)
 create mode 100644 lib/std/test/utf.myr

diff --git a/lib/std/chartype.myr b/lib/std/chartype.myr
index dd31e200..bf01d9ae 100644
--- a/lib/std/chartype.myr
+++ b/lib/std/chartype.myr
@@ -26,6 +26,8 @@ pkg std =
 	const totitle	: (c : char -> char)
 
 	generic charval : (c : char, base : int -> @a::(integral,numeric))
+
+	const cellwidth	: (c : char -> int)
 ;;
 
 extern const put	: (fmt : byte[:], args : ... -> size)
@@ -1061,6 +1063,445 @@ const rtotitle1 = [
 	0x01f3, 499	/* dz Dz */
 ]
 
+/*
+ * Generated by
+ *
+ * uniset cat:Me,Mn,Cf | \
+ *      sed -r 's/^([0-9a-f]+)[.][.]([0-9a-f]+)$/\t0x\1, 0x\2,/' |\
+ *      sed -r 's/^([0-9a-f]+)$/\t0x\1, 0x\1,/'
+ */
+const width0 = [
+	0xad, 0xad,
+	0x300, 0x36f,
+	0x483, 0x489,
+	0x591, 0x5bd,
+	0x5bf, 0x5bf,
+	0x5c1, 0x5c2,
+	0x5c4, 0x5c5,
+	0x5c7, 0x5c7,
+	0x600, 0x605,
+	0x610, 0x61a,
+	0x61c, 0x61c,
+	0x64b, 0x65f,
+	0x670, 0x670,
+	0x6d6, 0x6dd,
+	0x6df, 0x6e4,
+	0x6e7, 0x6e8,
+	0x6ea, 0x6ed,
+	0x70f, 0x70f,
+	0x711, 0x711,
+	0x730, 0x74a,
+	0x7a6, 0x7b0,
+	0x7eb, 0x7f3,
+	0x816, 0x819,
+	0x81b, 0x823,
+	0x825, 0x827,
+	0x829, 0x82d,
+	0x859, 0x85b,
+	0x8d4, 0x902,
+	0x93a, 0x93a,
+	0x93c, 0x93c,
+	0x941, 0x948,
+	0x94d, 0x94d,
+	0x951, 0x957,
+	0x962, 0x963,
+	0x981, 0x981,
+	0x9bc, 0x9bc,
+	0x9c1, 0x9c4,
+	0x9cd, 0x9cd,
+	0x9e2, 0x9e3,
+	0xa01, 0xa02,
+	0xa3c, 0xa3c,
+	0xa41, 0xa42,
+	0xa47, 0xa48,
+	0xa4b, 0xa4d,
+	0xa51, 0xa51,
+	0xa70, 0xa71,
+	0xa75, 0xa75,
+	0xa81, 0xa82,
+	0xabc, 0xabc,
+	0xac1, 0xac5,
+	0xac7, 0xac8,
+	0xacd, 0xacd,
+	0xae2, 0xae3,
+	0xafa, 0xaff,
+	0xb01, 0xb01,
+	0xb3c, 0xb3c,
+	0xb3f, 0xb3f,
+	0xb41, 0xb44,
+	0xb4d, 0xb4d,
+	0xb56, 0xb56,
+	0xb62, 0xb63,
+	0xb82, 0xb82,
+	0xbc0, 0xbc0,
+	0xbcd, 0xbcd,
+	0xc00, 0xc00,
+	0xc3e, 0xc40,
+	0xc46, 0xc48,
+	0xc4a, 0xc4d,
+	0xc55, 0xc56,
+	0xc62, 0xc63,
+	0xc81, 0xc81,
+	0xcbc, 0xcbc,
+	0xcbf, 0xcbf,
+	0xcc6, 0xcc6,
+	0xccc, 0xccd,
+	0xce2, 0xce3,
+	0xd00, 0xd01,
+	0xd3b, 0xd3c,
+	0xd41, 0xd44,
+	0xd4d, 0xd4d,
+	0xd62, 0xd63,
+	0xdca, 0xdca,
+	0xdd2, 0xdd4,
+	0xdd6, 0xdd6,
+	0xe31, 0xe31,
+	0xe34, 0xe3a,
+	0xe47, 0xe4e,
+	0xeb1, 0xeb1,
+	0xeb4, 0xeb9,
+	0xebb, 0xebc,
+	0xec8, 0xecd,
+	0xf18, 0xf19,
+	0xf35, 0xf35,
+	0xf37, 0xf37,
+	0xf39, 0xf39,
+	0xf71, 0xf7e,
+	0xf80, 0xf84,
+	0xf86, 0xf87,
+	0xf8d, 0xf97,
+	0xf99, 0xfbc,
+	0xfc6, 0xfc6,
+	0x102d, 0x1030,
+	0x1032, 0x1037,
+	0x1039, 0x103a,
+	0x103d, 0x103e,
+	0x1058, 0x1059,
+	0x105e, 0x1060,
+	0x1071, 0x1074,
+	0x1082, 0x1082,
+	0x1085, 0x1086,
+	0x108d, 0x108d,
+	0x109d, 0x109d,
+	0x135d, 0x135f,
+	0x1712, 0x1714,
+	0x1732, 0x1734,
+	0x1752, 0x1753,
+	0x1772, 0x1773,
+	0x17b4, 0x17b5,
+	0x17b7, 0x17bd,
+	0x17c6, 0x17c6,
+	0x17c9, 0x17d3,
+	0x17dd, 0x17dd,
+	0x180b, 0x180e,
+	0x1885, 0x1886,
+	0x18a9, 0x18a9,
+	0x1920, 0x1922,
+	0x1927, 0x1928,
+	0x1932, 0x1932,
+	0x1939, 0x193b,
+	0x1a17, 0x1a18,
+	0x1a1b, 0x1a1b,
+	0x1a56, 0x1a56,
+	0x1a58, 0x1a5e,
+	0x1a60, 0x1a60,
+	0x1a62, 0x1a62,
+	0x1a65, 0x1a6c,
+	0x1a73, 0x1a7c,
+	0x1a7f, 0x1a7f,
+	0x1ab0, 0x1abe,
+	0x1b00, 0x1b03,
+	0x1b34, 0x1b34,
+	0x1b36, 0x1b3a,
+	0x1b3c, 0x1b3c,
+	0x1b42, 0x1b42,
+	0x1b6b, 0x1b73,
+	0x1b80, 0x1b81,
+	0x1ba2, 0x1ba5,
+	0x1ba8, 0x1ba9,
+	0x1bab, 0x1bad,
+	0x1be6, 0x1be6,
+	0x1be8, 0x1be9,
+	0x1bed, 0x1bed,
+	0x1bef, 0x1bf1,
+	0x1c2c, 0x1c33,
+	0x1c36, 0x1c37,
+	0x1cd0, 0x1cd2,
+	0x1cd4, 0x1ce0,
+	0x1ce2, 0x1ce8,
+	0x1ced, 0x1ced,
+	0x1cf4, 0x1cf4,
+	0x1cf8, 0x1cf9,
+	0x1dc0, 0x1df9,
+	0x1dfb, 0x1dff,
+	0x200b, 0x200f,
+	0x202a, 0x202e,
+	0x2060, 0x2064,
+	0x2066, 0x206f,
+	0x20d0, 0x20f0,
+	0x2cef, 0x2cf1,
+	0x2d7f, 0x2d7f,
+	0x2de0, 0x2dff,
+	0x302a, 0x302d,
+	0x3099, 0x309a,
+	0xa66f, 0xa672,
+	0xa674, 0xa67d,
+	0xa69e, 0xa69f,
+	0xa6f0, 0xa6f1,
+	0xa802, 0xa802,
+	0xa806, 0xa806,
+	0xa80b, 0xa80b,
+	0xa825, 0xa826,
+	0xa8c4, 0xa8c5,
+	0xa8e0, 0xa8f1,
+	0xa926, 0xa92d,
+	0xa947, 0xa951,
+	0xa980, 0xa982,
+	0xa9b3, 0xa9b3,
+	0xa9b6, 0xa9b9,
+	0xa9bc, 0xa9bc,
+	0xa9e5, 0xa9e5,
+	0xaa29, 0xaa2e,
+	0xaa31, 0xaa32,
+	0xaa35, 0xaa36,
+	0xaa43, 0xaa43,
+	0xaa4c, 0xaa4c,
+	0xaa7c, 0xaa7c,
+	0xaab0, 0xaab0,
+	0xaab2, 0xaab4,
+	0xaab7, 0xaab8,
+	0xaabe, 0xaabf,
+	0xaac1, 0xaac1,
+	0xaaec, 0xaaed,
+	0xaaf6, 0xaaf6,
+	0xabe5, 0xabe5,
+	0xabe8, 0xabe8,
+	0xabed, 0xabed,
+	0xfb1e, 0xfb1e,
+	0xfe00, 0xfe0f,
+	0xfe20, 0xfe2f,
+	0xfeff, 0xfeff,
+	0xfff9, 0xfffb,
+	0x101fd, 0x101fd,
+	0x102e0, 0x102e0,
+	0x10376, 0x1037a,
+	0x10a01, 0x10a03,
+	0x10a05, 0x10a06,
+	0x10a0c, 0x10a0f,
+	0x10a38, 0x10a3a,
+	0x10a3f, 0x10a3f,
+	0x10ae5, 0x10ae6,
+	0x11001, 0x11001,
+	0x11038, 0x11046,
+	0x1107f, 0x11081,
+	0x110b3, 0x110b6,
+	0x110b9, 0x110ba,
+	0x110bd, 0x110bd,
+	0x11100, 0x11102,
+	0x11127, 0x1112b,
+	0x1112d, 0x11134,
+	0x11173, 0x11173,
+	0x11180, 0x11181,
+	0x111b6, 0x111be,
+	0x111ca, 0x111cc,
+	0x1122f, 0x11231,
+	0x11234, 0x11234,
+	0x11236, 0x11237,
+	0x1123e, 0x1123e,
+	0x112df, 0x112df,
+	0x112e3, 0x112ea,
+	0x11300, 0x11301,
+	0x1133c, 0x1133c,
+	0x11340, 0x11340,
+	0x11366, 0x1136c,
+	0x11370, 0x11374,
+	0x11438, 0x1143f,
+	0x11442, 0x11444,
+	0x11446, 0x11446,
+	0x114b3, 0x114b8,
+	0x114ba, 0x114ba,
+	0x114bf, 0x114c0,
+	0x114c2, 0x114c3,
+	0x115b2, 0x115b5,
+	0x115bc, 0x115bd,
+	0x115bf, 0x115c0,
+	0x115dc, 0x115dd,
+	0x11633, 0x1163a,
+	0x1163d, 0x1163d,
+	0x1163f, 0x11640,
+	0x116ab, 0x116ab,
+	0x116ad, 0x116ad,
+	0x116b0, 0x116b5,
+	0x116b7, 0x116b7,
+	0x1171d, 0x1171f,
+	0x11722, 0x11725,
+	0x11727, 0x1172b,
+	0x11a01, 0x11a06,
+	0x11a09, 0x11a0a,
+	0x11a33, 0x11a38,
+	0x11a3b, 0x11a3e,
+	0x11a47, 0x11a47,
+	0x11a51, 0x11a56,
+	0x11a59, 0x11a5b,
+	0x11a8a, 0x11a96,
+	0x11a98, 0x11a99,
+	0x11c30, 0x11c36,
+	0x11c38, 0x11c3d,
+	0x11c3f, 0x11c3f,
+	0x11c92, 0x11ca7,
+	0x11caa, 0x11cb0,
+	0x11cb2, 0x11cb3,
+	0x11cb5, 0x11cb6,
+	0x11d31, 0x11d36,
+	0x11d3a, 0x11d3a,
+	0x11d3c, 0x11d3d,
+	0x11d3f, 0x11d45,
+	0x11d47, 0x11d47,
+	0x16af0, 0x16af4,
+	0x16b30, 0x16b36,
+	0x16f8f, 0x16f92,
+	0x1bc9d, 0x1bc9e,
+	0x1bca0, 0x1bca3,
+	0x1d167, 0x1d169,
+	0x1d173, 0x1d182,
+	0x1d185, 0x1d18b,
+	0x1d1aa, 0x1d1ad,
+	0x1d242, 0x1d244,
+	0x1da00, 0x1da36,
+	0x1da3b, 0x1da6c,
+	0x1da75, 0x1da75,
+	0x1da84, 0x1da84,
+	0x1da9b, 0x1da9f,
+	0x1daa1, 0x1daaf,
+	0x1e000, 0x1e006,
+	0x1e008, 0x1e018,
+	0x1e01b, 0x1e021,
+	0x1e023, 0x1e024,
+	0x1e026, 0x1e02a,
+	0x1e8d0, 0x1e8d6,
+	0x1e944, 0x1e94a,
+	0xe0001, 0xe0001,
+	0xe0020, 0xe007f,
+	0xe0100, 0xe01ef,
+]
+
+/*
+ * Generated by
+ *
+ * uniset eaw:W,F - cat:Me,Mn,Cf | \
+ *      sed -r 's/^([0-9a-f]+)[.][.]([0-9a-f]+)$/\t0x\1, 0x\2,/' | \
+ *      sed -r 's/^([0-9a-f]+)$/\t0x\1, 0x\1,/'
+ */
+const width2 = [
+	0x1100, 0x115f,
+	0x231a, 0x231b,
+	0x2329, 0x232a,
+	0x23e9, 0x23ec,
+	0x23f0, 0x23f0,
+	0x23f3, 0x23f3,
+	0x25fd, 0x25fe,
+	0x2614, 0x2615,
+	0x2648, 0x2653,
+	0x267f, 0x267f,
+	0x2693, 0x2693,
+	0x26a1, 0x26a1,
+	0x26aa, 0x26ab,
+	0x26bd, 0x26be,
+	0x26c4, 0x26c5,
+	0x26ce, 0x26ce,
+	0x26d4, 0x26d4,
+	0x26ea, 0x26ea,
+	0x26f2, 0x26f3,
+	0x26f5, 0x26f5,
+	0x26fa, 0x26fa,
+	0x26fd, 0x26fd,
+	0x2705, 0x2705,
+	0x270a, 0x270b,
+	0x2728, 0x2728,
+	0x274c, 0x274c,
+	0x274e, 0x274e,
+	0x2753, 0x2755,
+	0x2757, 0x2757,
+	0x2795, 0x2797,
+	0x27b0, 0x27b0,
+	0x27bf, 0x27bf,
+	0x2b1b, 0x2b1c,
+	0x2b50, 0x2b50,
+	0x2b55, 0x2b55,
+	0x2e80, 0x2e99,
+	0x2e9b, 0x2ef3,
+	0x2f00, 0x2fd5,
+	0x2ff0, 0x2ffb,
+	0x3000, 0x3029,
+	0x302e, 0x303e,
+	0x3041, 0x3096,
+	0x309b, 0x30ff,
+	0x3105, 0x312e,
+	0x3131, 0x318e,
+	0x3190, 0x31ba,
+	0x31c0, 0x31e3,
+	0x31f0, 0x321e,
+	0x3220, 0x3247,
+	0x3250, 0x32fe,
+	0x3300, 0x4dbf,
+	0x4e00, 0xa48c,
+	0xa490, 0xa4c6,
+	0xa960, 0xa97c,
+	0xac00, 0xd7a3,
+	0xf900, 0xfaff,
+	0xfe10, 0xfe19,
+	0xfe30, 0xfe52,
+	0xfe54, 0xfe66,
+	0xfe68, 0xfe6b,
+	0xff01, 0xff60,
+	0xffe0, 0xffe6,
+	0x16fe0, 0x16fe1,
+	0x17000, 0x187ec,
+	0x18800, 0x18af2,
+	0x1b000, 0x1b11e,
+	0x1b170, 0x1b2fb,
+	0x1f004, 0x1f004,
+	0x1f0cf, 0x1f0cf,
+	0x1f18e, 0x1f18e,
+	0x1f191, 0x1f19a,
+	0x1f200, 0x1f202,
+	0x1f210, 0x1f23b,
+	0x1f240, 0x1f248,
+	0x1f250, 0x1f251,
+	0x1f260, 0x1f265,
+	0x1f300, 0x1f320,
+	0x1f32d, 0x1f335,
+	0x1f337, 0x1f37c,
+	0x1f37e, 0x1f393,
+	0x1f3a0, 0x1f3ca,
+	0x1f3cf, 0x1f3d3,
+	0x1f3e0, 0x1f3f0,
+	0x1f3f4, 0x1f3f4,
+	0x1f3f8, 0x1f43e,
+	0x1f440, 0x1f440,
+	0x1f442, 0x1f4fc,
+	0x1f4ff, 0x1f53d,
+	0x1f54b, 0x1f54e,
+	0x1f550, 0x1f567,
+	0x1f57a, 0x1f57a,
+	0x1f595, 0x1f596,
+	0x1f5a4, 0x1f5a4,
+	0x1f5fb, 0x1f64f,
+	0x1f680, 0x1f6c5,
+	0x1f6cc, 0x1f6cc,
+	0x1f6d0, 0x1f6d2,
+	0x1f6eb, 0x1f6ec,
+	0x1f6f4, 0x1f6f8,
+	0x1f910, 0x1f93e,
+	0x1f940, 0x1f94c,
+	0x1f950, 0x1f96b,
+	0x1f980, 0x1f997,
+	0x1f9c0, 0x1f9c0,
+	0x1f9d0, 0x1f9e6,
+	0x20000, 0x2fffd,
+	0x30000, 0x3fffd,
+]
+
 const findc = {c, t, n, nelt, ret
 	var p, m
 
@@ -1245,3 +1686,32 @@ generic charval = {c, base -> @a::(numeric,integral)
 	;;
 	-> v
 }
+
+const cellwidth = { c : char
+	var l
+	/*
+	 * Follows the general idea described at
+	 * http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c
+	 */
+	if c == 0
+		-> 0
+	;;
+
+	if c == -1 || c < 0x20 || (c >= 0x7f && c <= 0x9f)
+		-> -1
+	;;
+
+	if findc(c, width0[:], width0.len/2, 2, &l)
+		if (c >= l[0] && c <= l[1])
+			-> 0
+		;;
+	;;
+
+	if findc(c, width2[:], width2.len/2, 2, &l)
+		if (c >= l[0] && c <= l[1])
+			-> 2
+		;;
+	;;
+
+	-> 1
+}
diff --git a/lib/std/fmt.myr b/lib/std/fmt.myr
index 08b814db..1f542d31 100644
--- a/lib/std/fmt.myr
+++ b/lib/std/fmt.myr
@@ -553,7 +553,7 @@ const strfmt = {sb, str, params
 			;;
 		;;
 	else
-		for i = 0; i < w - graphemewidth(str); i++
+		for i = 0; i < w - strcellwidth(str); i++
 			sbputc(sb, p)
 		;;
 		sbputs(sb, str)
@@ -564,14 +564,6 @@ const isprint = {b
 	-> b >= (' ' : byte) && b < ('~' : byte)
 }
 
-/*
-Hah. like we're going to put in the work to actually
-count graphemes.
-*/
-const graphemewidth = {str
-	-> str.len
-}
-
 const digitchars = [
 	'0','1','2','3','4',
 	'5','6','7','8','9',
diff --git a/lib/std/test/chartype.myr b/lib/std/test/chartype.myr
index d0df1d2b..30426e67 100644
--- a/lib/std/test/chartype.myr
+++ b/lib/std/test/chartype.myr
@@ -20,4 +20,22 @@ const main = {
 	std.assert(!std.isalnum('!'), "! should not be isalnum\n")
 	std.assert(!std.isspace('@'), "@ should not be isspace\n")
 	std.assert(!std.isblank('@'), "@ should not be isblank\n")
+
+	std.assert(std.cellwidth(std.Badchar) == -1, "Badchar should have width -1\n")
+	std.assert(std.cellwidth((0 : char)) == 0, "U+0000 should have width 0\n")
+	std.assert(std.cellwidth('') == -1, "^E should have width -1\n")
+	std.assert(std.cellwidth('a') == 1, "'a' should have width 1\n")
+	std.assert(std.cellwidth('ê') == 1, "'ê' should have width 1\n")
+	std.assert(std.cellwidth('̀') == 0, "U+300 should have width 0\n")
+	std.assert(std.cellwidth('ϼ') == 1,  "ϼ should have width 1\n")
+	std.assert(std.cellwidth('Ї') == 1, "Ї should have width 1\n")
+	std.assert(std.cellwidth('⊲') == 1, "⊲ should have width 1\n")
+	std.assert(std.cellwidth('　') == 2, "U+3000 should have width 2\n")
+	std.assert(std.cellwidth('ギ') == 2, "ギ should have width 2\n")
+	std.assert(std.cellwidth('匌') == 2, "匌 should have width 2\n")
+	std.assert(std.cellwidth('­') == 0, "U+00AD should have width 0\n")
+	std.assert(std.cellwidth('ࠠ') == 0, "U+820 should have width 0\n")
+	std.assert(std.cellwidth('־') == 1, "U+5BE should have width 1\n")
+	std.assert(std.cellwidth('ֿ') == 0, "U+5BF should have width 0\n")
+	std.assert(std.cellwidth('׀') == 1, "U+5C0 should have width 1\n")
 }
diff --git a/lib/std/test/fmt.myr b/lib/std/test/fmt.myr
index 5d0cfa83..c1a17acc 100644
--- a/lib/std/test/fmt.myr
+++ b/lib/std/test/fmt.myr
@@ -56,6 +56,10 @@ const builtins = {
 	check("\\n\\r\\xff", "{e}", "\n\r\xff")
 	check("{}barbaz", "{{}}bar{}", "baz")
 	check("{barbaz}", "{{bar{}}}", "baz")
+	check("      Tlön", "{w=10}", "Tlön")
+	check("     háček", "{w=10}", "háček")
+	check("_____即是多多即", "{w=15,p=_}", "即是多多即")
+	check("   τῶν ῾Ελλήνων", "{w=15}", "τῶν ῾Ελλήνων")
 	check("abcd", "{}", "abcd")
 	check("123", "{}", 123)
 	check("7b", "{x}", 123)
diff --git a/lib/std/test/utf.myr b/lib/std/test/utf.myr
new file mode 100644
index 0000000000000000000000000000000000000000..4ac25d79704f0b359a279cd83f8f42069fb90743
GIT binary patch
literal 1305
zcma)+F>ljQ5XV{LPjSlBR*;f{KnxkG45)w@V9nw<4z=po@a!r=2q|uo7N}8M3sK3T
zR3OwP6i5oBB_s@0BnBG0AK_t9iOnB@a~w6OdXh8vy?gJ@zyF=@<V8&cP0w+hpemXU
z1zu7h1&_Gc^c39Ti!ggPJvRqa(_9Rr61=8~M4t#uO(%jV%S9=t&rihjs+#3Vd=gSA
zxN;uiMWQPAVBiEb51C;=CLW)RAcc&JEXLsNL1t-H(TOU9FwYZS&_$v}r^uhnhU^&@
z8@(g^tRRSrt^u#)Ku`-=Ns+Lc0#6pk(CKeDRj1;Zq1a`X*eE38WArwAZ+_N#^<MYz
z-C-jnUS$!_21aln{8|oSNfr#fV>Akmw%~X91wQqVb&19LFKP^C{%8x4r$lCUr!k{`
z-By(gw|E^#R}+YIA3GO0u>Eb?S$9@w=PNjsej_+kXy+3+rGCRPXs6|rgZt3e3JaXU
zd@@`tc6Pe26H#1<9BlU^9Iv=v+_u|wo49`iw}EE+*mOI%A0!fqp$rZ`OD6r0NU|&m
zkxGA`l}?&_p7G&i_w%2%re~O*(e;e&q*u1R@^^1(e<*|<V+!548L2_-Hm$t`YVT3|
zfZBCx@8Dr4uxe{)h2EM)?YFe{8bd?L<TbV=SyV(VQq;Ff``}yVs&7>{(O7QbvQ)(z
t3ytTma4GHj)>G5BDnIb>BnUE$;0BG=_rtRB2f!>FbCB{XDPSItxqlrZ1D5~*

literal 0
HcmV?d00001

diff --git a/lib/std/utf.myr b/lib/std/utf.myr
index 6c655a33..439254ca 100644
--- a/lib/std/utf.myr
+++ b/lib/std/utf.myr
@@ -1,3 +1,5 @@
+use "extremum"
+use "chartype"
 use "die"
 use "types"
 
@@ -12,6 +14,7 @@ pkg std =
 	const decode	: (buf : byte[:] -> char)
 	const strstep	: (str : byte[:] -> (char, byte[:]))
 
+	const strcellwidth : (str : byte[:] -> size)
 ;;
 
 const charlen = {c
@@ -101,3 +104,29 @@ const strstep = {str
 
 	-> ((chr : char), str[len:])
 }
+
+const strcellwidth = {str
+	var s : byte[:] = str
+	var c : char = Badchar
+	var n : size = 0
+
+	while s.len > 0
+		(c, s) = strstep(s)
+		if c == Badchar
+			/* Something will probably be printed as U+FFFD */
+			n++
+		elif c < 0x20
+			/* Control characters take 0 cells */
+		elif c < 0x7f
+			/* Bog standard ASCII takes 1 cell */
+			n++
+		elif c == 0x7f
+			/* DEL is like a control character */
+		else
+			/* It's not ASCII, so ask chartype what to do */
+			n += (abs(cellwidth(c)) : size)
+		;;
+	;;
+
+	-> n
+}
-- 
2.14.3