Implement typo detection for literals.

1 files changed, 173 insertions, 0 deletions

diff --git a/typo.c b/typo.c
new file mode 100644
index 0000000..e3b8e43
--- /dev/null
+++ b/typo.c
@@ -0,0 +1,173 @@
+/*********************************************************************
+ * bfs                                                               *
+ * Copyright (C) 2016 Tavian Barnes <tavianator@tavianator.com>      *
+ *                                                                   *
+ * This program is free software. It comes without any warranty, to  *
+ * the extent permitted by applicable law. You can redistribute it   *
+ * and/or modify it under the terms of the Do What The Fuck You Want *
+ * To Public License, Version 2, as published by Sam Hocevar. See    *
+ * the COPYING file or http://www.wtfpl.net/ for more details.       *
+ *********************************************************************/
+
+#include "typo.h"
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct coords {
+	int x, y;
+};
+
+// Assume QWERTY layout for now
+static const struct coords key_coords[UCHAR_MAX] = {
+	['`']  = { 0,  0},
+	['~']  = { 0,  0},
+	['1']  = { 3,  0},
+	['!']  = { 3,  0},
+	['2']  = { 6,  0},
+	['@']  = { 6,  0},
+	['3']  = { 9,  0},
+	['#']  = { 9,  0},
+	['4']  = {12,  0},
+	['$']  = {12,  0},
+	['5']  = {15,  0},
+	['%']  = {15,  0},
+	['6']  = {18,  0},
+	['^']  = {18,  0},
+	['7']  = {21,  0},
+	['&']  = {21,  0},
+	['8']  = {24,  0},
+	['*']  = {24,  0},
+	['9']  = {27,  0},
+	['(']  = {27,  0},
+	['0']  = {30,  0},
+	[')']  = {30,  0},
+	['-']  = {33,  0},
+	['_']  = {33,  0},
+	['=']  = {36,  0},
+	['+']  = {36,  0},
+
+	['\t'] = { 1,  3},
+	['q']  = { 4,  3},
+	['Q']  = { 4,  3},
+	['w']  = { 7,  3},
+	['W']  = { 7,  3},
+	['e']  = {10,  3},
+	['E']  = {10,  3},
+	['r']  = {13,  3},
+	['R']  = {13,  3},
+	['t']  = {16,  3},
+	['T']  = {16,  3},
+	['y']  = {19,  3},
+	['Y']  = {19,  3},
+	['u']  = {22,  3},
+	['U']  = {22,  3},
+	['i']  = {25,  3},
+	['I']  = {25,  3},
+	['o']  = {28,  3},
+	['O']  = {28,  3},
+	['p']  = {31,  3},
+	['P']  = {31,  3},
+	['[']  = {34,  3},
+	['{']  = {34,  3},
+	[']']  = {37,  3},
+	['}']  = {37,  3},
+	['\\'] = {40,  3},
+	['|']  = {40,  3},
+
+	['a']  = { 5,  6},
+	['A']  = { 5,  6},
+	['s']  = { 8,  6},
+	['S']  = { 8,  6},
+	['d']  = {11,  6},
+	['D']  = {11,  6},
+	['f']  = {14,  6},
+	['F']  = {14,  6},
+	['g']  = {17,  6},
+	['G']  = {17,  6},
+	['h']  = {20,  6},
+	['H']  = {20,  6},
+	['j']  = {23,  6},
+	['J']  = {23,  6},
+	['k']  = {26,  6},
+	['K']  = {26,  6},
+	['l']  = {29,  6},
+	['L']  = {29,  6},
+	[';']  = {32,  6},
+	[':']  = {32,  6},
+	['\''] = {35,  6},
+	['"']  = {35,  6},
+	['\n'] = {38,  6},
+
+	['z']  = { 6,  9},
+	['Z']  = { 6,  9},
+	['x']  = { 9,  9},
+	['X']  = { 9,  9},
+	['c']  = {12,  9},
+	['C']  = {12,  9},
+	['v']  = {15,  9},
+	['V']  = {15,  9},
+	['b']  = {18,  9},
+	['B']  = {18,  9},
+	['n']  = {21,  9},
+	['N']  = {21,  9},
+	['m']  = {24,  9},
+	['M']  = {24,  9},
+	[',']  = {27,  9},
+	['<']  = {27,  9},
+	['.']  = {30,  9},
+	['>']  = {30,  9},
+	['/']  = {33,  9},
+	['?']  = {33,  9},
+
+	[' ']  = {18, 12},
+};
+
+static int char_distance(char a, char b) {
+	const struct coords *ac = &key_coords[(unsigned char)a], *bc = &key_coords[(unsigned char)b];
+	int dx = abs(ac->x - bc->x);
+	int dy = abs(ac->y - bc->y);
+	return dx + dy;
+}
+
+int typo_distance(const char *actual, const char *expected) {
+	// This is the Wagner-Fischer algorithm for Levenshtein distance, using
+	// Manhattan distance on the keyboard for individual characters.
+
+	const int insert_cost = 12;
+
+	size_t rows = strlen(actual) + 1;
+	size_t cols = strlen(expected) + 1;
+
+	int arr0[cols], arr1[cols];
+	int *row0 = arr0, *row1 = arr1;
+
+	for (size_t j = 0; j < cols; ++j) {
+		row0[j] = insert_cost * j;
+	}
+
+	for (size_t i = 1; i < rows; ++i) {
+		row1[0] = row0[0] + insert_cost;
+
+		char a = actual[i - 1];
+		for (size_t j = 1; j < cols; ++j) {
+			char b = expected[j - 1];
+			int cost = row0[j - 1] + char_distance(a, b);
+			int del_cost = row0[j] + insert_cost;
+			if (del_cost < cost) {
+				cost = del_cost;
+			}
+			int ins_cost = row1[j - 1] + insert_cost;
+			if (ins_cost < cost) {
+				cost = ins_cost;
+			}
+			row1[j] = cost;
+		}
+
+		int *tmp = row0;
+		row0 = row1;
+		row1 = tmp;
+	}
+
+	return row0[cols - 1];
+}