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Replace if/loop conditions dependency on input signals with ternary operator. #217

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Replace if/loop conditions dependency on input signals with ternary operator. #217

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70 changes: 23 additions & 47 deletions packages/circuits/lib/bigint-func.circom
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Original file line number Diff line number Diff line change
Expand Up @@ -104,15 +104,16 @@ function poly_interp(len, v) {

// 1 if true, 0 if false
function long_gt(n, k, a, b) {
var is_set = 0;
var is_gt = 0;
for (var i = k - 1; i >= 0; i--) {
if (a[i] > b[i]) {
return 1;
}
if (a[i] < b[i]) {
return 0;
}
is_gt = is_set == 0 && a[i] > b[i] ? 1 : is_gt;
is_set = is_set == 0 && a[i] > b[i] ? 1 : is_set;

// if <=, set the is_set var to True
is_set = is_set == 0 && a[i] < b[i] ? 1 : is_set;
}
return 0;
return is_gt;
}

// n bits per register
Expand All @@ -124,21 +125,11 @@ function long_sub(n, k, a, b) {
var borrow[100];
for (var i = 0; i < k; i++) {
if (i == 0) {
if (a[i] >= b[i]) {
diff[i] = a[i] - b[i];
borrow[i] = 0;
} else {
diff[i] = a[i] - b[i] + (1 << n);
borrow[i] = 1;
}
diff[i] = a[i] >= b[i] ? a[i] - b[i] : a[i] - b[i] + (1 << n);
borrow[i] = a[i] >= b[i] ? 0 : 1;
} else {
if (a[i] >= b[i] + borrow[i - 1]) {
diff[i] = a[i] - b[i] - borrow[i - 1];
borrow[i] = 0;
} else {
diff[i] = (1 << n) + a[i] - b[i] - borrow[i - 1];
borrow[i] = 1;
}
diff[i] = a[i] >= b[i] + borrow[i - 1] ? a[i] - b[i] - borrow[i - 1] : (1 << n) + a[i] - b[i] - borrow[i - 1];
borrow[i] = a[i] >= b[i] + borrow[i - 1] ? 0 : 1;
}
}
return diff;
Expand Down Expand Up @@ -168,13 +159,6 @@ function long_scalar_mult(n, k, a, b) {
// implements algorithm of https://people.eecs.berkeley.edu/~fateman/282/F%20Wright%20notes/week4.pdf
function long_div(n, k, m, a, b){
var out[2][100];
m += k;
while (b[k-1] == 0) {
out[1][k] = 0;
k--;
assert(k > 0);
}
m -= k;

var remainder[100];
for (var i = 0; i < m + k; i++) {
Expand Down Expand Up @@ -224,21 +208,15 @@ function long_div(n, k, m, a, b){
// 0 <= a < (2**n) * b
function short_div_norm(n, k, a, b) {
var qhat = (a[k] * (1 << n) + a[k - 1]) \ b[k - 1];
if (qhat > (1 << n) - 1) {
qhat = (1 << n) - 1;
}
var v = (1 << n) - 1;
qhat = qhat > v ? v : qhat;

var mult[100] = long_scalar_mult(n, k, qhat, b);
if (long_gt(n, k + 1, mult, a) == 1) {
mult = long_sub(n, k + 1, mult, b);
if (long_gt(n, k + 1, mult, a) == 1) {
return qhat - 2;
} else {
return qhat - 1;
}
} else {
return qhat;
}
var cond = long_gt(n, k + 1, mult, a);
var mult2[100] = long_sub(n, k + 1, mult, b);
var cond2 = long_gt(n, k + 1, mult2, a);
var qhat2 = cond2 == 1 ? qhat - 2 : qhat - 1;
return cond == 1 ? qhat2 : qhat;
}

// n bits per register
Expand All @@ -254,11 +232,9 @@ function short_div(n, k, a, b) {
// k + 1 registers now
var norm_b[100] = long_scalar_mult(n, k, scale, b);

var ret;
if (norm_b[k] != 0) {
ret = short_div_norm(n, k + 1, norm_a, norm_b);
} else {
ret = short_div_norm(n, k, norm_a, norm_b);
}
var ret_a = short_div_norm(n, k + 1, norm_a, norm_b);
var ret_b = short_div_norm(n, k, norm_a, norm_b);
var ret = norm_b[k] != 0 ? ret_a : ret_b;

return ret;
}