96 lines
2.3 KiB
Plaintext
96 lines
2.3 KiB
Plaintext
/*
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Copyright 2018 0KIMS association.
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This file is part of circom (Zero Knowledge Circuit Compiler).
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circom is a free software: you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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circom is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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You should have received a copy of the GNU General Public License
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along with circom. If not, see <https://www.gnu.org/licenses/>.
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*/
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/*
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Binary Sum
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==========
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This component creates a binary sum componet of ops operands and n bits each operand.
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e is Number of carries: Depends on the number of operands in the input.
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Main Constraint:
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in[0][0] * 2^0 + in[0][1] * 2^1 + ..... + in[0][n-1] * 2^(n-1) +
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+ in[1][0] * 2^0 + in[1][1] * 2^1 + ..... + in[1][n-1] * 2^(n-1) +
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+ ..
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+ in[ops-1][0] * 2^0 + in[ops-1][1] * 2^1 + ..... + in[ops-1][n-1] * 2^(n-1) +
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===
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out[0] * 2^0 + out[1] * 2^1 + + out[n+e-1] *2(n+e-1)
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To waranty binary outputs:
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out[0] * (out[0] - 1) === 0
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out[1] * (out[0] - 1) === 0
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.
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.
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.
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out[n+e-1] * (out[n+e-1] - 1) == 0
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*/
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/*
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This function calculates the number of extra bits in the output to do the full sum.
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*/
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/* a must be < Nq/2, where Nq is the number of elements in the scalar field */
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function nbits(a) {
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var n = 1;
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var r = 0;
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while (n-1<a) {
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r++;
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n *= 2;
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}
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return r;
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}
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/* n must be such that (2**(n+1) -2) < Nq/ops, where Nq is the number of bits in the scalar field */
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template BinSum(n, ops) {
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var nout = nbits((2**n -1)*ops);
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signal input in[ops][n];
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signal output out[nout];
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var lin = 0;
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var lout = 0;
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var k;
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var j;
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for (k=0; k<n; k++) {
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for (j=0; j<ops; j++) {
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lin += in[j][k] * 2**k;
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}
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}
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for (k=0; k<nout; k++) {
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out[k] <-- (lin >> k) & 1;
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// Ensure out is binary
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out[k] * (out[k] - 1) === 0;
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lout += out[k] * 2**k;
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}
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// Ensure the sum;
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lin === lout;
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}
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