Much faster (and smaller) method of mapping RGB colour to an xterm(1)

colour, from Avi Halachmi.

1 files changed, 52 insertions, 302 deletions

diff --git a/colour.c b/colour.c
index b349e2a5..99b2b3b0 100644
--- a/colour.c
+++ b/colour.c
@@ -2,6 +2,7 @@
 
 /*
  * Copyright (c) 2008 Nicholas Marriott <nicholas.marriott@gmail.com>
+ * Copyright (c) 2016 Avi Halachmi <avihpit@yahoo.com>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -24,316 +25,65 @@
 
 #include "tmux.h"
 
-/*
- * Colour to string conversion functions. Bit 8 of the colour means it is one
- * of the 256 colour palette.
- */
-
-struct colour_rgb {
-	u_char  i;
-	u_char	r;
-	u_char	g;
-	u_char	b;
-};
-
-const struct colour_rgb colour_from_256[] = {
-	{   0, 0x00, 0x00, 0x00 }, {   1, 0x00, 0x00, 0x5f },
-	{   2, 0x00, 0x00, 0x87 }, {   3, 0x00, 0x00, 0xaf },
-	{   4, 0x00, 0x00, 0xd7 }, {   5, 0x00, 0x00, 0xff },
-	{   6, 0x00, 0x5f, 0x00 }, {   7, 0x00, 0x5f, 0x5f },
-	{   8, 0x00, 0x5f, 0x87 }, {   9, 0x00, 0x5f, 0xaf },
-	{  10, 0x00, 0x5f, 0xd7 }, {  11, 0x00, 0x5f, 0xff },
-	{  12, 0x00, 0x87, 0x00 }, {  13, 0x00, 0x87, 0x5f },
-	{  14, 0x00, 0x87, 0x87 }, {  15, 0x00, 0x87, 0xaf },
-	{  16, 0x00, 0x87, 0xd7 }, {  17, 0x00, 0x87, 0xff },
-	{  18, 0x00, 0xaf, 0x00 }, {  19, 0x00, 0xaf, 0x5f },
-	{  20, 0x00, 0xaf, 0x87 }, {  21, 0x00, 0xaf, 0xaf },
-	{  22, 0x00, 0xaf, 0xd7 }, {  23, 0x00, 0xaf, 0xff },
-	{  24, 0x00, 0xd7, 0x00 }, {  25, 0x00, 0xd7, 0x5f },
-	{  26, 0x00, 0xd7, 0x87 }, {  27, 0x00, 0xd7, 0xaf },
-	{  28, 0x00, 0xd7, 0xd7 }, {  29, 0x00, 0xd7, 0xff },
-	{  30, 0x00, 0xff, 0x00 }, {  31, 0x00, 0xff, 0x5f },
-	{  32, 0x00, 0xff, 0x87 }, {  33, 0x00, 0xff, 0xaf },
-	{  34, 0x00, 0xff, 0xd7 }, {  35, 0x00, 0xff, 0xff },
-	{  36, 0x5f, 0x00, 0x00 }, {  37, 0x5f, 0x00, 0x5f },
-	{  38, 0x5f, 0x00, 0x87 }, {  39, 0x5f, 0x00, 0xaf },
-	{  40, 0x5f, 0x00, 0xd7 }, {  41, 0x5f, 0x00, 0xff },
-	{  42, 0x5f, 0x5f, 0x00 }, {  43, 0x5f, 0x5f, 0x5f },
-	{  44, 0x5f, 0x5f, 0x87 }, {  45, 0x5f, 0x5f, 0xaf },
-	{  46, 0x5f, 0x5f, 0xd7 }, {  47, 0x5f, 0x5f, 0xff },
-	{  48, 0x5f, 0x87, 0x00 }, {  49, 0x5f, 0x87, 0x5f },
-	{  50, 0x5f, 0x87, 0x87 }, {  51, 0x5f, 0x87, 0xaf },
-	{  52, 0x5f, 0x87, 0xd7 }, {  53, 0x5f, 0x87, 0xff },
-	{  54, 0x5f, 0xaf, 0x00 }, {  55, 0x5f, 0xaf, 0x5f },
-	{  56, 0x5f, 0xaf, 0x87 }, {  57, 0x5f, 0xaf, 0xaf },
-	{  58, 0x5f, 0xaf, 0xd7 }, {  59, 0x5f, 0xaf, 0xff },
-	{  60, 0x5f, 0xd7, 0x00 }, {  61, 0x5f, 0xd7, 0x5f },
-	{  62, 0x5f, 0xd7, 0x87 }, {  63, 0x5f, 0xd7, 0xaf },
-	{  64, 0x5f, 0xd7, 0xd7 }, {  65, 0x5f, 0xd7, 0xff },
-	{  66, 0x5f, 0xff, 0x00 }, {  67, 0x5f, 0xff, 0x5f },
-	{  68, 0x5f, 0xff, 0x87 }, {  69, 0x5f, 0xff, 0xaf },
-	{  70, 0x5f, 0xff, 0xd7 }, {  71, 0x5f, 0xff, 0xff },
-	{  72, 0x87, 0x00, 0x00 }, {  73, 0x87, 0x00, 0x5f },
-	{  74, 0x87, 0x00, 0x87 }, {  75, 0x87, 0x00, 0xaf },
-	{  76, 0x87, 0x00, 0xd7 }, {  77, 0x87, 0x00, 0xff },
-	{  78, 0x87, 0x5f, 0x00 }, {  79, 0x87, 0x5f, 0x5f },
-	{  80, 0x87, 0x5f, 0x87 }, {  81, 0x87, 0x5f, 0xaf },
-	{  82, 0x87, 0x5f, 0xd7 }, {  83, 0x87, 0x5f, 0xff },
-	{  84, 0x87, 0x87, 0x00 }, {  85, 0x87, 0x87, 0x5f },
-	{  86, 0x87, 0x87, 0x87 }, {  87, 0x87, 0x87, 0xaf },
-	{  88, 0x87, 0x87, 0xd7 }, {  89, 0x87, 0x87, 0xff },
-	{  90, 0x87, 0xaf, 0x00 }, {  91, 0x87, 0xaf, 0x5f },
-	{  92, 0x87, 0xaf, 0x87 }, {  93, 0x87, 0xaf, 0xaf },
-	{  94, 0x87, 0xaf, 0xd7 }, {  95, 0x87, 0xaf, 0xff },
-	{  96, 0x87, 0xd7, 0x00 }, {  97, 0x87, 0xd7, 0x5f },
-	{  98, 0x87, 0xd7, 0x87 }, {  99, 0x87, 0xd7, 0xaf },
-	{ 100, 0x87, 0xd7, 0xd7 }, { 101, 0x87, 0xd7, 0xff },
-	{ 102, 0x87, 0xff, 0x00 }, { 103, 0x87, 0xff, 0x5f },
-	{ 104, 0x87, 0xff, 0x87 }, { 105, 0x87, 0xff, 0xaf },
-	{ 106, 0x87, 0xff, 0xd7 }, { 107, 0x87, 0xff, 0xff },
-	{ 108, 0xaf, 0x00, 0x00 }, { 109, 0xaf, 0x00, 0x5f },
-	{ 110, 0xaf, 0x00, 0x87 }, { 111, 0xaf, 0x00, 0xaf },
-	{ 112, 0xaf, 0x00, 0xd7 }, { 113, 0xaf, 0x00, 0xff },
-	{ 114, 0xaf, 0x5f, 0x00 }, { 115, 0xaf, 0x5f, 0x5f },
-	{ 116, 0xaf, 0x5f, 0x87 }, { 117, 0xaf, 0x5f, 0xaf },
-	{ 118, 0xaf, 0x5f, 0xd7 }, { 119, 0xaf, 0x5f, 0xff },
-	{ 120, 0xaf, 0x87, 0x00 }, { 121, 0xaf, 0x87, 0x5f },
-	{ 122, 0xaf, 0x87, 0x87 }, { 123, 0xaf, 0x87, 0xaf },
-	{ 124, 0xaf, 0x87, 0xd7 }, { 125, 0xaf, 0x87, 0xff },
-	{ 126, 0xaf, 0xaf, 0x00 }, { 127, 0xaf, 0xaf, 0x5f },
-	{ 128, 0xaf, 0xaf, 0x87 }, { 129, 0xaf, 0xaf, 0xaf },
-	{ 130, 0xaf, 0xaf, 0xd7 }, { 131, 0xaf, 0xaf, 0xff },
-	{ 132, 0xaf, 0xd7, 0x00 }, { 133, 0xaf, 0xd7, 0x5f },
-	{ 134, 0xaf, 0xd7, 0x87 }, { 135, 0xaf, 0xd7, 0xaf },
-	{ 136, 0xaf, 0xd7, 0xd7 }, { 137, 0xaf, 0xd7, 0xff },
-	{ 138, 0xaf, 0xff, 0x00 }, { 139, 0xaf, 0xff, 0x5f },
-	{ 140, 0xaf, 0xff, 0x87 }, { 141, 0xaf, 0xff, 0xaf },
-	{ 142, 0xaf, 0xff, 0xd7 }, { 143, 0xaf, 0xff, 0xff },
-	{ 144, 0xd7, 0x00, 0x00 }, { 145, 0xd7, 0x00, 0x5f },
-	{ 146, 0xd7, 0x00, 0x87 }, { 147, 0xd7, 0x00, 0xaf },
-	{ 148, 0xd7, 0x00, 0xd7 }, { 149, 0xd7, 0x00, 0xff },
-	{ 150, 0xd7, 0x5f, 0x00 }, { 151, 0xd7, 0x5f, 0x5f },
-	{ 152, 0xd7, 0x5f, 0x87 }, { 153, 0xd7, 0x5f, 0xaf },
-	{ 154, 0xd7, 0x5f, 0xd7 }, { 155, 0xd7, 0x5f, 0xff },
-	{ 156, 0xd7, 0x87, 0x00 }, { 157, 0xd7, 0x87, 0x5f },
-	{ 158, 0xd7, 0x87, 0x87 }, { 159, 0xd7, 0x87, 0xaf },
-	{ 160, 0xd7, 0x87, 0xd7 }, { 161, 0xd7, 0x87, 0xff },
-	{ 162, 0xd7, 0xaf, 0x00 }, { 163, 0xd7, 0xaf, 0x5f },
-	{ 164, 0xd7, 0xaf, 0x87 }, { 165, 0xd7, 0xaf, 0xaf },
-	{ 166, 0xd7, 0xaf, 0xd7 }, { 167, 0xd7, 0xaf, 0xff },
-	{ 168, 0xd7, 0xd7, 0x00 }, { 169, 0xd7, 0xd7, 0x5f },
-	{ 170, 0xd7, 0xd7, 0x87 }, { 171, 0xd7, 0xd7, 0xaf },
-	{ 172, 0xd7, 0xd7, 0xd7 }, { 173, 0xd7, 0xd7, 0xff },
-	{ 174, 0xd7, 0xff, 0x00 }, { 175, 0xd7, 0xff, 0x5f },
-	{ 176, 0xd7, 0xff, 0x87 }, { 177, 0xd7, 0xff, 0xaf },
-	{ 178, 0xd7, 0xff, 0xd7 }, { 179, 0xd7, 0xff, 0xff },
-	{ 180, 0xff, 0x00, 0x00 }, { 181, 0xff, 0x00, 0x5f },
-	{ 182, 0xff, 0x00, 0x87 }, { 183, 0xff, 0x00, 0xaf },
-	{ 184, 0xff, 0x00, 0xd7 }, { 185, 0xff, 0x00, 0xff },
-	{ 186, 0xff, 0x5f, 0x00 }, { 187, 0xff, 0x5f, 0x5f },
-	{ 188, 0xff, 0x5f, 0x87 }, { 189, 0xff, 0x5f, 0xaf },
-	{ 190, 0xff, 0x5f, 0xd7 }, { 191, 0xff, 0x5f, 0xff },
-	{ 192, 0xff, 0x87, 0x00 }, { 193, 0xff, 0x87, 0x5f },
-	{ 194, 0xff, 0x87, 0x87 }, { 195, 0xff, 0x87, 0xaf },
-	{ 196, 0xff, 0x87, 0xd7 }, { 197, 0xff, 0x87, 0xff },
-	{ 198, 0xff, 0xaf, 0x00 }, { 199, 0xff, 0xaf, 0x5f },
-	{ 200, 0xff, 0xaf, 0x87 }, { 201, 0xff, 0xaf, 0xaf },
-	{ 202, 0xff, 0xaf, 0xd7 }, { 203, 0xff, 0xaf, 0xff },
-	{ 204, 0xff, 0xd7, 0x00 }, { 205, 0xff, 0xd7, 0x5f },
-	{ 206, 0xff, 0xd7, 0x87 }, { 207, 0xff, 0xd7, 0xaf },
-	{ 208, 0xff, 0xd7, 0xd7 }, { 209, 0xff, 0xd7, 0xff },
-	{ 210, 0xff, 0xff, 0x00 }, { 211, 0xff, 0xff, 0x5f },
-	{ 212, 0xff, 0xff, 0x87 }, { 213, 0xff, 0xff, 0xaf },
-	{ 214, 0xff, 0xff, 0xd7 }, { 215, 0xff, 0xff, 0xff },
-	{ 216, 0x08, 0x08, 0x08 }, { 217, 0x12, 0x12, 0x12 },
-	{ 218, 0x1c, 0x1c, 0x1c }, { 219, 0x26, 0x26, 0x26 },
-	{ 220, 0x30, 0x30, 0x30 }, { 221, 0x3a, 0x3a, 0x3a },
-	{ 222, 0x44, 0x44, 0x44 }, { 223, 0x4e, 0x4e, 0x4e },
-	{ 224, 0x58, 0x58, 0x58 }, { 225, 0x62, 0x62, 0x62 },
-	{ 226, 0x6c, 0x6c, 0x6c }, { 227, 0x76, 0x76, 0x76 },
-	{ 228, 0x80, 0x80, 0x80 }, { 229, 0x8a, 0x8a, 0x8a },
-	{ 230, 0x94, 0x94, 0x94 }, { 231, 0x9e, 0x9e, 0x9e },
-	{ 232, 0xa8, 0xa8, 0xa8 }, { 233, 0xb2, 0xb2, 0xb2 },
-	{ 234, 0xbc, 0xbc, 0xbc }, { 235, 0xc6, 0xc6, 0xc6 },
-	{ 236, 0xd0, 0xd0, 0xd0 }, { 237, 0xda, 0xda, 0xda },
-	{ 238, 0xe4, 0xe4, 0xe4 }, { 239, 0xee, 0xee, 0xee },
-};
-const struct colour_rgb colour_to_256[] = {
-	{   0, 0x00, 0x00, 0x00 }, {   1, 0x00, 0x00, 0x5f },
-	{   2, 0x00, 0x00, 0x87 }, {   3, 0x00, 0x00, 0xaf },
-	{   4, 0x00, 0x00, 0xd7 }, {   5, 0x00, 0x00, 0xff },
-	{   6, 0x00, 0x5f, 0x00 }, {   7, 0x00, 0x5f, 0x5f },
-	{   8, 0x00, 0x5f, 0x87 }, {   9, 0x00, 0x5f, 0xaf },
-	{  10, 0x00, 0x5f, 0xd7 }, {  11, 0x00, 0x5f, 0xff },
-	{  12, 0x00, 0x87, 0x00 }, {  13, 0x00, 0x87, 0x5f },
-	{  14, 0x00, 0x87, 0x87 }, {  15, 0x00, 0x87, 0xaf },
-	{  16, 0x00, 0x87, 0xd7 }, {  17, 0x00, 0x87, 0xff },
-	{  18, 0x00, 0xaf, 0x00 }, {  19, 0x00, 0xaf, 0x5f },
-	{  20, 0x00, 0xaf, 0x87 }, {  21, 0x00, 0xaf, 0xaf },
-	{  22, 0x00, 0xaf, 0xd7 }, {  23, 0x00, 0xaf, 0xff },
-	{  24, 0x00, 0xd7, 0x00 }, {  25, 0x00, 0xd7, 0x5f },
-	{  26, 0x00, 0xd7, 0x87 }, {  27, 0x00, 0xd7, 0xaf },
-	{  28, 0x00, 0xd7, 0xd7 }, {  29, 0x00, 0xd7, 0xff },
-	{  30, 0x00, 0xff, 0x00 }, {  31, 0x00, 0xff, 0x5f },
-	{  32, 0x00, 0xff, 0x87 }, {  33, 0x00, 0xff, 0xaf },
-	{  34, 0x00, 0xff, 0xd7 }, {  35, 0x00, 0xff, 0xff },
-	{ 216, 0x08, 0x08, 0x08 }, { 217, 0x12, 0x12, 0x12 },
-	{ 218, 0x1c, 0x1c, 0x1c }, { 219, 0x26, 0x26, 0x26 },
-	{ 220, 0x30, 0x30, 0x30 }, { 221, 0x3a, 0x3a, 0x3a },
-	{ 222, 0x44, 0x44, 0x44 }, { 223, 0x4e, 0x4e, 0x4e },
-	{ 224, 0x58, 0x58, 0x58 }, {  36, 0x5f, 0x00, 0x00 },
-	{  37, 0x5f, 0x00, 0x5f }, {  38, 0x5f, 0x00, 0x87 },
-	{  39, 0x5f, 0x00, 0xaf }, {  40, 0x5f, 0x00, 0xd7 },
-	{  41, 0x5f, 0x00, 0xff }, {  42, 0x5f, 0x5f, 0x00 },
-	{  43, 0x5f, 0x5f, 0x5f }, {  44, 0x5f, 0x5f, 0x87 },
-	{  45, 0x5f, 0x5f, 0xaf }, {  46, 0x5f, 0x5f, 0xd7 },
-	{  47, 0x5f, 0x5f, 0xff }, {  48, 0x5f, 0x87, 0x00 },
-	{  49, 0x5f, 0x87, 0x5f }, {  50, 0x5f, 0x87, 0x87 },
-	{  51, 0x5f, 0x87, 0xaf }, {  52, 0x5f, 0x87, 0xd7 },
-	{  53, 0x5f, 0x87, 0xff }, {  54, 0x5f, 0xaf, 0x00 },
-	{  55, 0x5f, 0xaf, 0x5f }, {  56, 0x5f, 0xaf, 0x87 },
-	{  57, 0x5f, 0xaf, 0xaf }, {  58, 0x5f, 0xaf, 0xd7 },
-	{  59, 0x5f, 0xaf, 0xff }, {  60, 0x5f, 0xd7, 0x00 },
-	{  61, 0x5f, 0xd7, 0x5f }, {  62, 0x5f, 0xd7, 0x87 },
-	{  63, 0x5f, 0xd7, 0xaf }, {  64, 0x5f, 0xd7, 0xd7 },
-	{  65, 0x5f, 0xd7, 0xff }, {  66, 0x5f, 0xff, 0x00 },
-	{  67, 0x5f, 0xff, 0x5f }, {  68, 0x5f, 0xff, 0x87 },
-	{  69, 0x5f, 0xff, 0xaf }, {  70, 0x5f, 0xff, 0xd7 },
-	{  71, 0x5f, 0xff, 0xff }, { 225, 0x62, 0x62, 0x62 },
-	{ 226, 0x6c, 0x6c, 0x6c }, { 227, 0x76, 0x76, 0x76 },
-	{ 228, 0x80, 0x80, 0x80 }, {  72, 0x87, 0x00, 0x00 },
-	{  73, 0x87, 0x00, 0x5f }, {  74, 0x87, 0x00, 0x87 },
-	{  75, 0x87, 0x00, 0xaf }, {  76, 0x87, 0x00, 0xd7 },
-	{  77, 0x87, 0x00, 0xff }, {  78, 0x87, 0x5f, 0x00 },
-	{  79, 0x87, 0x5f, 0x5f }, {  80, 0x87, 0x5f, 0x87 },
-	{  81, 0x87, 0x5f, 0xaf }, {  82, 0x87, 0x5f, 0xd7 },
-	{  83, 0x87, 0x5f, 0xff }, {  84, 0x87, 0x87, 0x00 },
-	{  85, 0x87, 0x87, 0x5f }, {  86, 0x87, 0x87, 0x87 },
-	{  87, 0x87, 0x87, 0xaf }, {  88, 0x87, 0x87, 0xd7 },
-	{  89, 0x87, 0x87, 0xff }, {  90, 0x87, 0xaf, 0x00 },
-	{  91, 0x87, 0xaf, 0x5f }, {  92, 0x87, 0xaf, 0x87 },
-	{  93, 0x87, 0xaf, 0xaf }, {  94, 0x87, 0xaf, 0xd7 },
-	{  95, 0x87, 0xaf, 0xff }, {  96, 0x87, 0xd7, 0x00 },
-	{  97, 0x87, 0xd7, 0x5f }, {  98, 0x87, 0xd7, 0x87 },
-	{  99, 0x87, 0xd7, 0xaf }, { 100, 0x87, 0xd7, 0xd7 },
-	{ 101, 0x87, 0xd7, 0xff }, { 102, 0x87, 0xff, 0x00 },
-	{ 103, 0x87, 0xff, 0x5f }, { 104, 0x87, 0xff, 0x87 },
-	{ 105, 0x87, 0xff, 0xaf }, { 106, 0x87, 0xff, 0xd7 },
-	{ 107, 0x87, 0xff, 0xff }, { 229, 0x8a, 0x8a, 0x8a },
-	{ 230, 0x94, 0x94, 0x94 }, { 231, 0x9e, 0x9e, 0x9e },
-	{ 232, 0xa8, 0xa8, 0xa8 }, { 108, 0xaf, 0x00, 0x00 },
-	{ 109, 0xaf, 0x00, 0x5f }, { 110, 0xaf, 0x00, 0x87 },
-	{ 111, 0xaf, 0x00, 0xaf }, { 112, 0xaf, 0x00, 0xd7 },
-	{ 113, 0xaf, 0x00, 0xff }, { 114, 0xaf, 0x5f, 0x00 },
-	{ 115, 0xaf, 0x5f, 0x5f }, { 116, 0xaf, 0x5f, 0x87 },
-	{ 117, 0xaf, 0x5f, 0xaf }, { 118, 0xaf, 0x5f, 0xd7 },
-	{ 119, 0xaf, 0x5f, 0xff }, { 120, 0xaf, 0x87, 0x00 },
-	{ 121, 0xaf, 0x87, 0x5f }, { 122, 0xaf, 0x87, 0x87 },
-	{ 123, 0xaf, 0x87, 0xaf }, { 124, 0xaf, 0x87, 0xd7 },
-	{ 125, 0xaf, 0x87, 0xff }, { 126, 0xaf, 0xaf, 0x00 },
-	{ 127, 0xaf, 0xaf, 0x5f }, { 128, 0xaf, 0xaf, 0x87 },
-	{ 129, 0xaf, 0xaf, 0xaf }, { 130, 0xaf, 0xaf, 0xd7 },
-	{ 131, 0xaf, 0xaf, 0xff }, { 132, 0xaf, 0xd7, 0x00 },
-	{ 133, 0xaf, 0xd7, 0x5f }, { 134, 0xaf, 0xd7, 0x87 },
-	{ 135, 0xaf, 0xd7, 0xaf }, { 136, 0xaf, 0xd7, 0xd7 },
-	{ 137, 0xaf, 0xd7, 0xff }, { 138, 0xaf, 0xff, 0x00 },
-	{ 139, 0xaf, 0xff, 0x5f }, { 140, 0xaf, 0xff, 0x87 },
-	{ 141, 0xaf, 0xff, 0xaf }, { 142, 0xaf, 0xff, 0xd7 },
-	{ 143, 0xaf, 0xff, 0xff }, { 233, 0xb2, 0xb2, 0xb2 },
-	{ 234, 0xbc, 0xbc, 0xbc }, { 235, 0xc6, 0xc6, 0xc6 },
-	{ 236, 0xd0, 0xd0, 0xd0 }, { 144, 0xd7, 0x00, 0x00 },
-	{ 145, 0xd7, 0x00, 0x5f }, { 146, 0xd7, 0x00, 0x87 },
-	{ 147, 0xd7, 0x00, 0xaf }, { 148, 0xd7, 0x00, 0xd7 },
-	{ 149, 0xd7, 0x00, 0xff }, { 150, 0xd7, 0x5f, 0x00 },
-	{ 151, 0xd7, 0x5f, 0x5f }, { 152, 0xd7, 0x5f, 0x87 },
-	{ 153, 0xd7, 0x5f, 0xaf }, { 154, 0xd7, 0x5f, 0xd7 },
-	{ 155, 0xd7, 0x5f, 0xff }, { 156, 0xd7, 0x87, 0x00 },
-	{ 157, 0xd7, 0x87, 0x5f }, { 158, 0xd7, 0x87, 0x87 },
-	{ 159, 0xd7, 0x87, 0xaf }, { 160, 0xd7, 0x87, 0xd7 },
-	{ 161, 0xd7, 0x87, 0xff }, { 162, 0xd7, 0xaf, 0x00 },
-	{ 163, 0xd7, 0xaf, 0x5f }, { 164, 0xd7, 0xaf, 0x87 },
-	{ 165, 0xd7, 0xaf, 0xaf }, { 166, 0xd7, 0xaf, 0xd7 },
-	{ 167, 0xd7, 0xaf, 0xff }, { 168, 0xd7, 0xd7, 0x00 },
-	{ 169, 0xd7, 0xd7, 0x5f }, { 170, 0xd7, 0xd7, 0x87 },
-	{ 171, 0xd7, 0xd7, 0xaf }, { 172, 0xd7, 0xd7, 0xd7 },
-	{ 173, 0xd7, 0xd7, 0xff }, { 174, 0xd7, 0xff, 0x00 },
-	{ 175, 0xd7, 0xff, 0x5f }, { 176, 0xd7, 0xff, 0x87 },
-	{ 177, 0xd7, 0xff, 0xaf }, { 178, 0xd7, 0xff, 0xd7 },
-	{ 179, 0xd7, 0xff, 0xff }, { 237, 0xda, 0xda, 0xda },
-	{ 238, 0xe4, 0xe4, 0xe4 }, { 239, 0xee, 0xee, 0xee },
-	{ 180, 0xff, 0x00, 0x00 }, { 181, 0xff, 0x00, 0x5f },
-	{ 182, 0xff, 0x00, 0x87 }, { 183, 0xff, 0x00, 0xaf },
-	{ 184, 0xff, 0x00, 0xd7 }, { 185, 0xff, 0x00, 0xff },
-	{ 186, 0xff, 0x5f, 0x00 }, { 187, 0xff, 0x5f, 0x5f },
-	{ 188, 0xff, 0x5f, 0x87 }, { 189, 0xff, 0x5f, 0xaf },
-	{ 190, 0xff, 0x5f, 0xd7 }, { 191, 0xff, 0x5f, 0xff },
-	{ 192, 0xff, 0x87, 0x00 }, { 193, 0xff, 0x87, 0x5f },
-	{ 194, 0xff, 0x87, 0x87 }, { 195, 0xff, 0x87, 0xaf },
-	{ 196, 0xff, 0x87, 0xd7 }, { 197, 0xff, 0x87, 0xff },
-	{ 198, 0xff, 0xaf, 0x00 }, { 199, 0xff, 0xaf, 0x5f },
-	{ 200, 0xff, 0xaf, 0x87 }, { 201, 0xff, 0xaf, 0xaf },
-	{ 202, 0xff, 0xaf, 0xd7 }, { 203, 0xff, 0xaf, 0xff },
-	{ 204, 0xff, 0xd7, 0x00 }, { 205, 0xff, 0xd7, 0x5f },
-	{ 206, 0xff, 0xd7, 0x87 }, { 207, 0xff, 0xd7, 0xaf },
-	{ 208, 0xff, 0xd7, 0xd7 }, { 209, 0xff, 0xd7, 0xff },
-	{ 210, 0xff, 0xff, 0x00 }, { 211, 0xff, 0xff, 0x5f },
-	{ 212, 0xff, 0xff, 0x87 }, { 213, 0xff, 0xff, 0xaf },
-	{ 214, 0xff, 0xff, 0xd7 }, { 215, 0xff, 0xff, 0xff },
-};
-
-int	colour_cmp_rgb(const void *, const void *);
-
-/* Compare function for bsearch(). */
-int
-colour_cmp_rgb(const void *lhs0, const void *rhs0)
+static int
+colour_dist_sq(int R, int G, int B, int r, int g, int b)
 {
-	const struct colour_rgb *lhs = lhs0, *rhs = rhs0;
-
-	if (lhs->r < rhs->r)
-		return (-1);
-	if (lhs->r > rhs->r)
-		return (1);
-
-	if (lhs->g < rhs->g)
-		return (-1);
-	if (lhs->g > rhs->g)
-		return (1);
+	return ((R - r) * (R - r) + (G - g) * (G - g) + (B - b) * (B - b));
+}
 
-	if (lhs->b < rhs->b)
-		return (-1);
-	if (lhs->b > rhs->b)
+static int
+colour_to_6cube(int v)
+{
+	if (v < 48)
+		return (0);
+	if (v < 114)
 		return (1);
-
-	return (0);
+	return ((v - 35) / 40);
 }
 
-/* Work out the nearest colour from the 256 colour set. */
+/*
+ * Convert an RGB triplet to the xterm(1) 256 colour palette.
+ *
+ * xterm provides a 6x6x6 colour cube (16 - 231) and 24 greys (232 - 255). We
+ * map our RGB colour to the closest in the cube, also work out the closest
+ * grey, and use the nearest of the two.
+ *
+ * Note that the xterm has much lower resolution for darker colors (they are
+ * not evenly spread out), so our 6 levels are not evenly spread: 0x0, 0x5f
+ * (95), 0x87 (135), 0xaf (175), 0xd7 (215) and 0xff (255). Greys are more
+ * evenly spread (8, 18, 28 ... 238).
+ */
 int
 colour_find_rgb(u_char r, u_char g, u_char b)
 {
-	struct colour_rgb	rgb = { .r = r, .g = g, .b = b }, *found;
-	u_int			distance, lowest, colour, i;
-	int			dr, dg, db;
-
-	found = bsearch(&rgb, colour_to_256, nitems(colour_to_256),
-	    sizeof colour_to_256[0], colour_cmp_rgb);
-	if (found != NULL)
-		return (16 + found->i);
-
-	colour = 16;
-	lowest = UINT_MAX;
-	for (i = 0; i < 240; i++) {
-		dr = (int)colour_from_256[i].r - r;
-		dg = (int)colour_from_256[i].g - g;
-		db = (int)colour_from_256[i].b - b;
-
-		distance = dr * dr + dg * dg + db * db;
-		if (distance < lowest) {
-			lowest = distance;
-			colour = 16 + i;
-		}
-	}
-	return (colour);
+	static const int	q2c[6] = { 0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff };
+	int			qr, qg, qb, cr, cg, cb, d, idx;
+	int			grey_avg, grey_idx, grey;
+
+	/* Map RGB to 6x6x6 cube. */
+	qr = colour_to_6cube(r); cr = q2c[qr];
+	qg = colour_to_6cube(g); cg = q2c[qg];
+	qb = colour_to_6cube(b); cb = q2c[qb];
+
+	/* If we have hit the colour exactly, return early. */
+	if (cr == r && cg == g && cb == b)
+		return (16 + (36 * qr) + (6 * qg) + qb);
+
+	/* Work out the closest grey (average of RGB). */
+	grey_avg = (r + g + b) / 3;
+	if (grey_avg > 238)
+		grey_idx = 23;
+	else
+		grey_idx = (grey_avg - 3) / 10;
+	grey = 8 + (10 * grey_idx);
+
+	/* Is grey or 6x6x6 colour closest? */
+	d = colour_dist_sq(cr, cg, cb, r, g, b);
+	if (colour_dist_sq(grey, grey, grey, r, g, b) < d)
+		idx = 232 + grey_idx;
+	else
+		idx = 16 + (36 * qr) + (6 * qg) + qb;
+	return (idx);
 }
 
 /* Set grid cell foreground colour. */