Benchmark of different ways of matching /@(-(?:[a-z]+-)+)?keyframes/ against a specific position in a string

bench.js

var testCases = [
    {
        input: new Array(4001).join('0123456789') + '@-webkit-keyframes {}' + new Array(4096).join('0123456789'),
        idx: 40000
    },
    {
        input: new Array(4001).join('0123456789') + '@keyframes {}' + new Array(4096).join('0123456789'),
        idx: 40000
    },
    {
        input: new Array(4001).join('0123456789') + '@invalid' + new Array(4001).join('0123456789') + '@keyframes{}',
        idx: 40000
    }
];

var atKeyframesRegExp = /@(-(?:[a-z]+-)+)?keyframes/g,
    atKeyframesAtStartRegExp = /^@(-(?:[a-z]+-)+)?keyframes/;

exports.compare = {
    'lastIndex + regExp.exec()': function () {
        testCases.forEach(function (testCase) {
            atKeyframesRegExp.lastIndex = testCase.idx;
	    var matchKeyframes = atKeyframesRegExp.exec(testCase.input);
            if (matchKeyframes && matchKeyframes.index === testCase.idx) {
                // Match! vendorPrefix === matchKeyframes[1]
            }
        });
    },
    'substring().match()': function () {
        testCases.forEach(function (testCase) {
	    var matchKeyframes = atKeyframesAtStartRegExp.exec(testCase.input.substring(testCase.idx));
            if (matchKeyframes) {
                // Match! vendorPrefix = matchKeyframes[1]
            }
        });
    },
    'low-level string gymnastics': function () {
        testCases.forEach(function (testCase) {
            var input = testCase.input;
            if (input.substring(testCase.idx, testCase.idx + '@keyframes'.length) === '@keyframes') {
                // Match! vendorPrefix = undefined
            } else {
                var j = testCase.idx + 1,
                    state = 0,
                    accept = false;
                OUTER: while (j < testCase.input.length) {
                    var ch = input[j];
                    switch (state) {
                    case 0:
                        if (ch === '-') {
                            state = 1;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 1:
                        if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 2:
                        if (ch >= 'a' && ch <= 'z') {
                            // Stay in state 2
                            break;
                        } else if (ch === '-') {
                            state = 3;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 3:
                        if (ch === 'k') {
                            state = 4;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 4:
                        if (ch === 'e') {
                            state = 5;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 5:
                        if (ch === 'y') {
                            state = 6;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 6:
                        if (ch === 'f') {
                            state = 7;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 7:
                        if (ch === 'r') {
                            state = 8;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 8:
                        if (ch === 'a') {
                            state = 9;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 9:
                        if (ch === 'm') {
                            state = 10;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 10:
                        if (ch === 'e') {
                            state = 11;
                            break;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    case 11:
                        if (ch === 's') {
                            accept = true;
                            break OUTER;
                        } else if (ch >= 'a' && ch <= 'z') {
                            state = 2;
                            break;
                        } else {
                            break OUTER;
                        }
                    }
                    j += 1;
                }
                var vendorPrefix;
                if (accept) {
                    // Match! vendorPrefix = testCase.input.substring(testCase.idx + 1, 1 + j - 'keyframes'.length);
                }
            }
        });
    }
};
require('bench').runMain();

results

benchmarking /home/andreas/work/gist-1855943/bench.js
Please be patient.
{ node: '0.4.13-pre',
  v8: '3.1.8.27',
  ares: '1.7.4',
  ev: '4.4',
  openssl: '0.9.8o' }
Scores: (bigger is better)

low-level string gymnastics
Raw:
 > 998.001998001998
 > 989.010989010989
 > 1013.986013986014
 > 999.000999000999
 > 1025.974025974026
Average (mean) 1005.1948051948053

substring().match()
Raw:
 > 41.62537165510406
 > 40.553907022749755
 > 40.75546719681908
 > 42.03323558162268
 > 40.0390625
Average (mean) 41.00140879125912

lastIndex + regExp.exec()
Raw:
 > 22.30843840931135
 > 22.660098522167488
 > 22.660098522167488
 > 22.22222222222222
 > 22.373540856031127
Average (mean) 22.444879706379936

Winner: low-level string gymnastics
Compared with next highest (substring().match()), it's:
95.92% faster
24.52 times as fast
1.39 order(s) of magnitude faster

Compared with the slowest (lastIndex + regExp.exec()), it's:
97.77% faster
44.79 times as fast
1.65 order(s) of magnitude faster

results with the last test case omitted

benchmarking /home/andreas/work/gist-1855943/bench.js
Please be patient.
{ node: '0.4.13-pre',
  v8: '3.1.8.27',
  ares: '1.7.4',
  ev: '4.4',
  openssl: '0.9.8o' }
Scores: (bigger is better)

lastIndex + regExp.exec()
Raw:
 > 2060.939060939061
 > 1980.01998001998
 > 1966.033966033966
 > 1926.073926073926
 > 2102.8971028971027
Average (mean) 2007.1928071928073

low-level string gymnastics
Raw:
 > 1171.828171828172
 > 1167.832167832168
 > 1195.8041958041958
 > 1219.7802197802198
 > 1170.8291708291708
Average (mean) 1185.2147852147853

substring().match()
Raw:
 > 55.50049554013875
 > 55.61072492552135
 > 54.509415262636274
 > 54.78087649402391
 > 54.40158259149357
Average (mean) 54.96061896276277

Winner: lastIndex + regExp.exec()
Compared with next highest (low-level string gymnastics), it's:
40.95% faster
1.69 times as fast
0.23 order(s) of magnitude faster

Compared with the slowest (substring().match()), it's:
97.26% faster
36.52 times as fast
1.56 order(s) of magnitude faster