mirror of https://gogs.blitter.com/RLabs/xs
101 lines
2.6 KiB
Go
101 lines
2.6 KiB
Go
// cbd.go - Centered binomial distribution.
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//
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// To the extent possible under law, Yawning Angel has waived all copyright
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// and related or neighboring rights to the software, using the Creative
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// Commons "CC0" public domain dedication. See LICENSE or
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// <http://creativecommons.org/publicdomain/zero/1.0/> for full details.
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package kyber
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// Load bytes into a 64-bit integer in little-endian order.
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func loadLittleEndian(x []byte, bytes int) uint64 {
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var r uint64
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for i, v := range x[:bytes] {
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r |= uint64(v) << (8 * uint(i))
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}
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return r
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}
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// Given an array of uniformly random bytes, compute polynomial with
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// coefficients distributed according to a centered binomial distribution
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// with parameter eta.
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func (p *poly) cbd(buf []byte, eta int) {
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hardwareAccelImpl.cbdFn(p, buf, eta)
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}
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func cbdRef(p *poly, buf []byte, eta int) {
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switch eta {
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case 3:
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var a, b [4]uint32
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for i := 0; i < kyberN/4; i++ {
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t := loadLittleEndian(buf[3*i:], 3)
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var d uint32
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for j := 0; j < 3; j++ {
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d += uint32((t >> uint(j)) & 0x249249)
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}
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a[0] = d & 0x7
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b[0] = (d >> 3) & 0x7
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a[1] = (d >> 6) & 0x7
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b[1] = (d >> 9) & 0x7
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a[2] = (d >> 12) & 0x7
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b[2] = (d >> 15) & 0x7
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a[3] = (d >> 18) & 0x7
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b[3] = (d >> 21)
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p.coeffs[4*i+0] = uint16(a[0] + kyberQ - b[0])
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p.coeffs[4*i+1] = uint16(a[1] + kyberQ - b[1])
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p.coeffs[4*i+2] = uint16(a[2] + kyberQ - b[2])
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p.coeffs[4*i+3] = uint16(a[3] + kyberQ - b[3])
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}
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case 4:
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var a, b [4]uint32
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for i := 0; i < kyberN/4; i++ {
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t := loadLittleEndian(buf[4*i:], 4)
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var d uint32
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for j := 0; j < 4; j++ {
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d += uint32((t >> uint(j)) & 0x11111111)
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}
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a[0] = d & 0xf
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b[0] = (d >> 4) & 0xf
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a[1] = (d >> 8) & 0xf
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b[1] = (d >> 12) & 0xf
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a[2] = (d >> 16) & 0xf
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b[2] = (d >> 20) & 0xf
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a[3] = (d >> 24) & 0xf
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b[3] = (d >> 28)
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p.coeffs[4*i+0] = uint16(a[0] + kyberQ - b[0])
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p.coeffs[4*i+1] = uint16(a[1] + kyberQ - b[1])
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p.coeffs[4*i+2] = uint16(a[2] + kyberQ - b[2])
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p.coeffs[4*i+3] = uint16(a[3] + kyberQ - b[3])
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}
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case 5:
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var a, b [4]uint64
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for i := 0; i < kyberN/4; i++ {
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t := loadLittleEndian(buf[5*i:], 5)
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var d uint64
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for j := 0; j < 5; j++ {
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d += (t >> uint(j)) & 0x0842108421
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}
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a[0] = d & 0x1f
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b[0] = (d >> 5) & 0x1f
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a[1] = (d >> 10) & 0x1f
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b[1] = (d >> 15) & 0x1f
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a[2] = (d >> 20) & 0x1f
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b[2] = (d >> 25) & 0x1f
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a[3] = (d >> 30) & 0x1f
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b[3] = (d >> 35)
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p.coeffs[4*i+0] = uint16(a[0] + kyberQ - b[0])
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p.coeffs[4*i+1] = uint16(a[1] + kyberQ - b[1])
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p.coeffs[4*i+2] = uint16(a[2] + kyberQ - b[2])
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p.coeffs[4*i+3] = uint16(a[3] + kyberQ - b[3])
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}
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default:
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panic("kyber: eta must be in {3,4,5}")
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}
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}
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