mirror of
https://github.com/v2fly/v2ray-core.git
synced 2024-09-05 19:44:32 -04:00
67 lines
1.4 KiB
Go
67 lines
1.4 KiB
Go
// +build noasm !amd64
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package internal
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// helper used for Uint128 representation
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type Uint128 struct {
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H, L uint64
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}
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// Adds 2 64bit digits in constant time.
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// Returns result and carry (1 or 0)
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func Addc64(cin, a, b uint64) (ret, cout uint64) {
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t := a + cin
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ret = b + t
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cout = ((a & b) | ((a | b) & (^ret))) >> 63
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return
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}
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// Substracts 2 64bit digits in constant time.
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// Returns result and borrow (1 or 0)
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func Subc64(bIn, a, b uint64) (ret, bOut uint64) {
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var tmp1 = a - b
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// Set bOut if bIn!=0 and tmp1==0 in constant time
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bOut = bIn & (1 ^ ((tmp1 | uint64(0-tmp1)) >> 63))
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// Constant time check if x<y
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bOut |= (a ^ ((a ^ b) | (uint64(a-b) ^ b))) >> 63
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ret = tmp1 - bIn
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return
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}
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// Multiplies 2 64bit digits in constant time
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func Mul64(a, b uint64) (res Uint128) {
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var al, bl, ah, bh, albl, albh, ahbl, ahbh uint64
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var res1, res2, res3 uint64
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var carry, maskL, maskH, temp uint64
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maskL = (^maskL) >> 32
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maskH = ^maskL
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al = a & maskL
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ah = a >> 32
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bl = b & maskL
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bh = b >> 32
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albl = al * bl
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albh = al * bh
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ahbl = ah * bl
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ahbh = ah * bh
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res.L = albl & maskL
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res1 = albl >> 32
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res2 = ahbl & maskL
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res3 = albh & maskL
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temp = res1 + res2 + res3
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carry = temp >> 32
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res.L ^= temp << 32
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res1 = ahbl >> 32
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res2 = albh >> 32
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res3 = ahbh & maskL
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temp = res1 + res2 + res3 + carry
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res.H = temp & maskL
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carry = temp & maskH
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res.H ^= (ahbh & maskH) + carry
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return
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}
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