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gcs: replace multiplication with shifts.

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This commit is contained in:
Christopher Jeffrey 2017-06-16 15:11:16 -07:00
parent b994c278f2
commit 3324d18f5f
No known key found for this signature in database
GPG Key ID: 8962AB9DE6666BBD
1 changed files with 8 additions and 11 deletions
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19
lib/utils/gcs.js
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@ -21,8 +21,7 @@ var DUMMY = Buffer.allocUnsafe(0);
function GCSFilter() {
this.n = 0;
this.p = 0;
this.modp = Int64(0);
this.modnp = Int64(0);
this.m = Int64(0);
this.data = DUMMY;
}
@ -41,7 +40,7 @@ GCSFilter.prototype.header = function header(prev) {
GCSFilter.prototype.match = function match(key, data) {
var br = new BitReader(this.data);
var term = siphash(data, key).imod(this.modnp);
var term = siphash(data, key).imod(this.m);
var last = Int64(0);
var value;
@ -75,7 +74,7 @@ GCSFilter.prototype.matchAny = function matchAny(key, items) {
for (i = 0; i < items.length; i++) {
item = items[i];
hash = siphash(item, key).imod(this.modnp);
hash = siphash(item, key).imod(this.m);
values.push(hash);
}
@ -125,7 +124,7 @@ GCSFilter.prototype.readU64 = function readU64(br) {
rem = br.readBits64(this.p);
return num.imul(this.modp).iadd(rem);
return num.ishln(this.p).iadd(rem);
};
GCSFilter.prototype.toBytes = function toBytes() {
@ -171,15 +170,14 @@ GCSFilter.prototype.fromData = function fromData(P, key, items) {
this.n = items.length;
this.p = P;
this.modp = Int64(1).ishln(this.p);
this.modnp = Int64(this.n).imul(this.modp);
this.m = Int64(this.n).ishln(this.p);
bw = new BitWriter();
for (i = 0; i < items.length; i++) {
item = items[i];
assert(Buffer.isBuffer(item));
hash = siphash(item, key).imod(this.modnp);
hash = siphash(item, key).imod(this.m);
values.push(hash);
}
@ -187,7 +185,7 @@ GCSFilter.prototype.fromData = function fromData(P, key, items) {
for (i = 0; i < values.length; i++) {
hash = values[i];
rem = hash.sub(last).iand(this.modp.subn(1));
rem = hash.sub(last).imaskn(this.p);
value = hash.sub(last).isub(rem).ishrn(this.p);
last = hash;
@ -214,8 +212,7 @@ GCSFilter.prototype.fromBytes = function fromBytes(N, P, data) {
this.n = N;
this.p = P;
this.modp = Int64(1).ishln(this.p);
this.modnp = Int64(this.n).imul(this.modp);
this.m = Int64(this.n).ishln(this.p);
this.data = data;
return this;