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Implement i/fft from ethspecs

This commit is contained in:
danielsanchezq 2024-06-07 17:54:50 +02:00
parent d7bafffbdc
commit 0488748d5d
2 changed files with 28 additions and 28 deletions
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46
da/kzg_rs/fft.py
View File

@ -1,37 +1,37 @@
from typing import Sequence
def _simple_ft(vals, modulus, roots_of_unity): from eth2spec.deneb.mainnet import BLSFieldElement
L = len(roots_of_unity)
o = []
for i in range(L):
last = 0
for j in range(L):
last += vals[j] * roots_of_unity[(i*j)%L]
o.append(last % modulus)
return o
def _fft(vals, modulus, roots_of_unity): def _fft(
if len(vals) == 4: vals: Sequence[BLSFieldElement],
return _simple_ft(vals, modulus, roots_of_unity) roots_of_unity: Sequence[BLSFieldElement],
modulus: int,
) -> Sequence[BLSFieldElement]:
if len(vals) == 1: if len(vals) == 1:
return vals return vals
L = _fft(vals[::2], modulus, roots_of_unity[::2]) L = _fft(vals[::2], roots_of_unity[::2], modulus)
R = _fft(vals[1::2], modulus, roots_of_unity[::2]) R = _fft(vals[1::2], roots_of_unity[::2], modulus)
o = [0 for _ in vals] o = [BLSFieldElement(0) for _ in vals]
for i, (x, y) in enumerate(zip(L, R)): for i, (x, y) in enumerate(zip(L, R)):
y_times_root = (y*roots_of_unity[i]) % modulus y_times_root = (int(y) * int(roots_of_unity[i])) % modulus
o[i] = (x+y_times_root) % modulus o[i] = BLSFieldElement((int(x) + y_times_root) % modulus)
o[i+len(L)] = (x-y_times_root+modulus) % modulus o[i + len(L)] = BLSFieldElement((int(x) - y_times_root + modulus) % modulus)
return o return o
def fft(vals, modulus, root_of_unity): def fft(vals, root_of_unity, modulus):
assert len(vals) == len(root_of_unity) assert len(vals) == len(root_of_unity)
return _fft(vals, modulus, root_of_unity) return _fft(vals, root_of_unity, modulus)
def ifft(vals, modulus, root_of_unity): def ifft(vals, root_of_unity, modulus):
assert len(vals) == len(root_of_unity) assert len(vals) == len(root_of_unity)
# modular inverse # modular inverse
invlen = pow(len(vals), -1, modulus) invlen = pow(len(vals), modulus-2, modulus)
return [(x * invlen) % modulus for x in _fft(vals, modulus, list(reversed(root_of_unity)))] return [
BLSFieldElement((int(x) * invlen) % modulus)
for x in _fft(
vals, [root_of_unity[0], *root_of_unity[:0:-1]], modulus
)
]

10
da/kzg_rs/test_fft.py
View File

@ -2,12 +2,12 @@ from unittest import TestCase
from da.kzg_rs.common import BLS_MODULUS from da.kzg_rs.common import BLS_MODULUS
from fft import fft, ifft from fft import fft, ifft
from eth2spec.eip7594.mainnet import fft_field, BLSFieldElement
class TestFFT(TestCase): class TestFFT(TestCase):
def test_fft_ifft(self): def test_fft_ifft(self):
roots_of_unity = [pow(2, i, BLS_MODULUS) for i in range(8)] roots_of_unity = [pow(23674694431658770659612952115660802947967373701506253797663184111817857449850, i, BLS_MODULUS) for i in range(1024)]
vals = list(BLSFieldElement(x) for x in range(8)) vals = list(x for x in range(1024))
vals_fft = fft_field(vals, roots_of_unity) vals_fft = fft(vals, roots_of_unity, BLS_MODULUS)
self.assertEqual(vals, fft_field(vals_fft, roots_of_unity, inv=True)) self.assertEqual(vals, ifft(vals_fft, roots_of_unity, BLS_MODULUS))