use*_*029 13 javascript iphone safari optimization hash
这是目前(到目前为止)iPhone 4S和iPhone 5上移动Safari上最快的Javascript SHA256实现.
/** @fileOverview Javascript SHA-256 implementation.
*
* An older version of this implementation is available in the public
* domain, but this one is (c) Emily Stark, Mike Hamburg, Dan Boneh,
* Stanford University 2008-2010 and BSD-licensed for liability
* reasons.
*
* Special thanks to Aldo Cortesi for pointing out several bugs in
* this code.
*
* @author Emily Stark
* @author Mike Hamburg
* @author Dan Boneh
*/
/**
* Context for a SHA-256 operation in progress.
* @constructor
* @class Secure Hash Algorithm, 256 bits.
*/
sjcl.hash.sha256 = function (hash) {
if (!this._key[0]) { this._precompute(); }
if (hash) {
this._h = hash._h.slice(0);
this._buffer = hash._buffer.slice(0);
this._length = hash._length;
} else {
this.reset();
}
};
/**
* Hash a string or an array of words.
* @static
* @param {bitArray|String} data the data to hash.
* @return {bitArray} The hash value, an array of 16 big-endian words.
*/
sjcl.hash.sha256.hash = function (data) {
return (new sjcl.hash.sha256()).update(data).finalize();
};
sjcl.hash.sha256.prototype = {
/**
* The hash's block size, in bits.
* @constant
*/
blockSize: 512,
/**
* Reset the hash state.
* @return this
*/
reset:function () {
this._h = this._init.slice(0);
this._buffer = [];
this._length = 0;
return this;
},
/**
* Input several words to the hash.
* @param {bitArray|String} data the data to hash.
* @return this
*/
update: function (data) {
if (typeof data === "string") {
data = sjcl.codec.utf8String.toBits(data);
}
var i, b = this._buffer = sjcl.bitArray.concat(this._buffer, data),
ol = this._length,
nl = this._length = ol + sjcl.bitArray.bitLength(data);
for (i = 512+ol & -512; i <= nl; i+= 512) {
this._block(b.splice(0,16));
}
return this;
},
/**
* Complete hashing and output the hash value.
* @return {bitArray} The hash value, an array of 8 big-endian words.
*/
finalize:function () {
var i, b = this._buffer, h = this._h;
// Round out and push the buffer
b = sjcl.bitArray.concat(b, [sjcl.bitArray.partial(1,1)]);
// Round out the buffer to a multiple of 16 words, less the 2 length words.
for (i = b.length + 2; i & 15; i++) {
b.push(0);
}
// append the length
b.push(Math.floor(this._length / 0x100000000));
b.push(this._length | 0);
while (b.length) {
this._block(b.splice(0,16));
}
this.reset();
return h;
},
/**
* The SHA-256 initialization vector, to be precomputed.
* @private
*/
_init:[],
/*
_init:[0x6a09e667,0xbb67ae85,0x3c6ef372,0xa54ff53a,0x510e527f,0x9b05688c,0x1f83d9ab,0x5be0cd19],
*/
/**
* The SHA-256 hash key, to be precomputed.
* @private
*/
_key:[],
/*
_key:
[0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2],
*/
/**
* Function to precompute _init and _key.
* @private
*/
_precompute: function () {
var i = 0, prime = 2, factor;
function frac(x) { return (x-Math.floor(x)) * 0x100000000 | 0; }
outer: for (; i<64; prime++) {
for (factor=2; factor*factor <= prime; factor++) {
if (prime % factor === 0) {
// not a prime
continue outer;
}
}
if (i<8) {
this._init[i] = frac(Math.pow(prime, 1/2));
}
this._key[i] = frac(Math.pow(prime, 1/3));
i++;
}
},
/**
* Perform one cycle of SHA-256.
* @param {bitArray} words one block of words.
* @private
*/
_block:function (words) {
var i, tmp, a, b,
w = words.slice(0),
h = this._h,
k = this._key,
h0 = h[0], h1 = h[1], h2 = h[2], h3 = h[3],
h4 = h[4], h5 = h[5], h6 = h[6], h7 = h[7];
/* Rationale for placement of |0 :
* If a value can overflow is original 32 bits by a factor of more than a few
* million (2^23 ish), there is a possibility that it might overflow the
* 53-bit mantissa and lose precision.
*
* To avoid this, we clamp back to 32 bits by |'ing with 0 on any value that
* propagates around the loop, and on the hash state h[]. I don't believe
* that the clamps on h4 and on h0 are strictly necessary, but it's close
* (for h4 anyway), and better safe than sorry.
*
* The clamps on h[] are necessary for the output to be correct even in the
* common case and for short inputs.
*/
for (i=0; i<64; i++) {
// load up the input word for this round
if (i<16) {
tmp = w[i];
} else {
a = w[(i+1 ) & 15];
b = w[(i+14) & 15];
tmp = w[i&15] = ((a>>>7 ^ a>>>18 ^ a>>>3 ^ a<<25 ^ a<<14) +
(b>>>17 ^ b>>>19 ^ b>>>10 ^ b<<15 ^ b<<13) +
w[i&15] + w[(i+9) & 15]) | 0;
}
tmp = (tmp + h7 + (h4>>>6 ^ h4>>>11 ^ h4>>>25 ^ h4<<26 ^ h4<<21 ^ h4<<7) + (h6 ^ h4&(h5^h6)) + k[i]); // | 0;
// shift register
h7 = h6; h6 = h5; h5 = h4;
h4 = h3 + tmp | 0;
h3 = h2; h2 = h1; h1 = h0;
h0 = (tmp + ((h1&h2) ^ (h3&(h1^h2))) + (h1>>>2 ^ h1>>>13 ^ h1>>>22 ^ h1<<30 ^ h1<<19 ^ h1<<10)) | 0;
}
h[0] = h[0]+h0 | 0;
h[1] = h[1]+h1 | 0;
h[2] = h[2]+h2 | 0;
h[3] = h[3]+h3 | 0;
h[4] = h[4]+h4 | 0;
h[5] = h[5]+h5 | 0;
h[6] = h[6]+h6 | 0;
h[7] = h[7]+h7 | 0;
}
};
我的问题是:如何优化这些以更好地执行(在移动Safari上)？
我试过从各个角度探讨它(函数内联,循环展开,优化内存管理等).我做的每件事似乎都会让表现变得更糟,而不是更好.我已经能够得到一些提高速度的桌面浏览器,而不是一个在移动Safari浏览器单%的增速.分析也不是很有帮助.
这引出了一些额外的问题:
如果谁是真正能够提供一个体面的加速(移动Safari浏览器)版本将赏金点奖励(与万维网的感恩永恒).我知道这是一个非常棘手的问题,但它也是一个非常重要的问题.
这个循环看起来非常像它的 C 语言版本，所以我怀疑它是否可以得到微小的改进。请注意，“预计算”功能似乎不是最理想的，可以通过多种方式进行改进。考虑到素数检查已完成 64 次，这可能很有用：
如果我正确理解你的算法，你应该有 2 作为特殊情况（首先处理），从 3 开始，然后执行 +=2 来减少一半。
在代码中：
outer: for (; i<64; prime++) {
if (prime % factor === 0) continue outer;
for (factor=3; factor*factor +1 <= prime; factor+=2) {
if (prime % factor === 0) {
// not a prime
continue outer;
}
}
如果您只是想判断一个数字是否是质数，更好（但仍然很简单）的方法是边做边构建列表，并且只检查已知的质数。如果您需要我在 javascript 中执行此操作（如果有任何用处），请告诉我。或者使用
primes = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331]
并用 primes[i] 替换 prime，删除所有素数生成循环
if (i<8) {
this._init[i] = frac(Math.pow(primes[i], 1/2));
}
this._key[i] = frac(Math.pow(primes[i], 1/3));
i++;