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Merge branch 'kw/mod-exp-complexity-func' into kw/modexp-abstraction

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This commit is contained in:
Kevaundray Wedderburn 2025-07-11 11:31:14 +01:00
commit a08c8a3550
1 changed files with 48 additions and 38 deletions
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86
core/vm/contracts.go
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@ -396,33 +396,40 @@ var (
// else: return x ** 2 // 16 + 480 * x - 199680
//
// where is x is max(length_of_MODULUS, length_of_BASE)
func byzantiumMultComplexity(x uint64) *uint256.Int {
func byzantiumMultComplexity(x uint64) uint256.Int {
switch {
case x <= 64:
return new(uint256.Int).SetUint64(x * x)
var z uint256.Int
z.SetUint64(x * x)
return z
case x <= 1024:
// x^2 / 4 + 96*x - 3072
result := x*x/4 + 96*x - 3072
return new(uint256.Int).SetUint64(result)
var z uint256.Int
z.SetUint64(result)
return z
default:
// For large x, use uint256 arithmetic to avoid overflow
// x^2 / 16 + 480*x - 199680
xUint := new(uint256.Int).SetUint64(x)
var xUint, xSquared, result uint256.Int
xUint.SetUint64(x)
// Calculate x^2
xSquared := new(uint256.Int).Mul(xUint, xUint)
xSquared.Mul(&xUint, &xUint)
// Calculate x^2 / 16 (right shift by 4 bits)
xSquaredDiv16 := new(uint256.Int).Rsh(xSquared, 4)
result.Rsh(&xSquared, 4)
// Calculate 480 * x
x480 := new(uint256.Int).Mul(xUint, u256_480)
var x480 uint256.Int
x480.Mul(&xUint, u256_480)
// Calculate 480 * x - 199680
x480Minus199680 := new(uint256.Int).Sub(x480, u256_199680)
x480.Sub(&x480, u256_199680)
// Add the two parts together
return new(uint256.Int).Add(xSquaredDiv16, x480Minus199680)
result.Add(&result, &x480)
return result
}
}
@ -433,13 +440,17 @@ func byzantiumMultComplexity(x uint64) *uint256.Int {
// ceiling(x/8)^2
//
// where is x is max(length_of_MODULUS, length_of_BASE)
func berlinMultComplexity(x uint64) *uint256.Int {
func berlinMultComplexity(x uint64) uint256.Int {
// TODO: The preceding line is too smart.
// TODO: The issue is that (x+7) / 8 can overflow
// TODO: if x > 2^64 - 7
// Safe ceiling division by 8 to avoid overflow
ceilDiv8 := (x >> 3) + ((x&7 + 7) >> 3) // safe ceil(x / 8)
z := new(uint256.Int).SetUint64(ceilDiv8)
return new(uint256.Int).Mul(z, z) // square without overflow
var z uint256.Int
z.SetUint64(ceilDiv8)
z.Mul(&z, &z)
return z
}
// Slow Bigint way (benchmark this)
@ -454,18 +465,19 @@ func berlinMultComplexity(x uint64) *uint256.Int {
//
// For x <= 32: returns 16
// For x > 32: returns 2 * ceiling(x/8)^2
func osakaMultComplexity(x uint64) *uint256.Int {
func osakaMultComplexity(x uint64) uint256.Int {
if x <= 32 {
return u256_16
return *u256_16
}
// For x > 32, return 2 * berlinMultComplexity(x)
berlinComplexity := berlinMultComplexity(x)
return new(uint256.Int).Lsh(berlinComplexity, 1) // 2 * berlinComplexity
result := berlinMultComplexity(x)
result.Lsh(&result, 1) // 2 * berlinComplexity
return result
}
// calculateIterationCount calculates the number of iterations for the modexp precompile.
// This is the adjusted exponent length used in gas calculation.
func calculateIterationCount(expLen uint64, expHead *uint256.Int, multiplier uint64) uint64 {
func calculateIterationCount(expLen uint64, expHead uint256.Int, multiplier uint64) uint64 {
var iterationCount uint64
// For large exponents (expLen > 32), add (expLen - 32) * multiplier
@ -483,8 +495,7 @@ func calculateIterationCount(expLen uint64, expHead *uint256.Int, multiplier uin
}
// byzantiumGasCalc calculates the gas cost for the modexp precompile using Byzantium rules.
func byzantiumGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint64 {
// Calculate max(baseLen, modLen)
func byzantiumGasCalc(baseLen, expLen, modLen uint64, expHead uint256.Int) uint64 {
maxLen := max(baseLen, modLen)
// Calculate multiplication complexity
@ -494,9 +505,10 @@ func byzantiumGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint
iterationCount := calculateIterationCount(expLen, expHead, byzantiumMultiplier)
// Calculate gas: (multComplexity * iterationCount) / byzantiumDivisor
iterCount := new(uint256.Int).SetUint64(iterationCount)
gas := new(uint256.Int).Mul(multComplexity, iterCount)
gas.Div(gas, u256_byzantiumDivisor)
var gas uint256.Int
gas.SetUint64(iterationCount)
gas.Mul(&multComplexity, &gas)
gas.Div(&gas, u256_byzantiumDivisor)
if !gas.IsUint64() {
return math.MaxUint64
@ -505,8 +517,7 @@ func byzantiumGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint
}
// berlinGasCalc calculates the gas cost for the modexp precompile using Berlin rules.
func berlinGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint64 {
// Calculate max(baseLen, modLen)
func berlinGasCalc(baseLen, expLen, modLen uint64, expHead uint256.Int) uint64 {
maxLen := max(baseLen, modLen)
// Calculate multiplication complexity
@ -516,9 +527,10 @@ func berlinGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint64
iterationCount := calculateIterationCount(expLen, expHead, berlinMultiplier)
// Calculate gas: (multComplexity * iterationCount) / berlinDivisor
iterCount := new(uint256.Int).SetUint64(iterationCount)
gas := new(uint256.Int).Mul(multComplexity, iterCount)
gas.Div(gas, u256_berlinDivisor)
var gas uint256.Int
gas.SetUint64(iterationCount)
gas.Mul(&multComplexity, &gas)
gas.Div(&gas, u256_berlinDivisor)
if !gas.IsUint64() {
return math.MaxUint64
@ -529,8 +541,7 @@ func berlinGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint64
}
// osakaGasCalc calculates the gas cost for the modexp precompile using Osaka rules.
func osakaGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint64 {
// Calculate max(baseLen, modLen)
func osakaGasCalc(baseLen, expLen, modLen uint64, expHead uint256.Int) uint64 {
maxLen := max(baseLen, modLen)
// Calculate multiplication complexity
@ -540,9 +551,10 @@ func osakaGasCalc(baseLen, expLen, modLen uint64, expHead *uint256.Int) uint64 {
iterationCount := calculateIterationCount(expLen, expHead, osakaMultiplier)
// Calculate gas: (multComplexity * iterationCount) / osakaDivisor
iterCount := new(uint256.Int).SetUint64(iterationCount)
gas := new(uint256.Int).Mul(multComplexity, iterCount)
gas.Div(gas, u256_osakaDivisor)
var gas uint256.Int
gas.SetUint64(iterationCount)
gas.Mul(&multComplexity, &gas)
gas.Div(&gas, u256_osakaDivisor)
if !gas.IsUint64() {
return math.MaxUint64
@ -581,15 +593,13 @@ func (c *bigModExp) RequiredGas(input []byte) uint64 {
}
// Retrieve the head 32 bytes of exp for the adjusted exponent length
var expHead *uint256.Int
if uint64(len(input)) <= baseLen {
expHead = new(uint256.Int)
} else {
var expHead uint256.Int
if uint64(len(input)) > baseLen {
if expLen > 32 {
expHead = new(uint256.Int).SetBytes(getData(input, baseLen, 32))
expHead.SetBytes(getData(input, baseLen, 32))
} else {
// TODO: Check that if expLen < baseLen, then getData will return an empty slice
expHead = new(uint256.Int).SetBytes(getData(input, baseLen, expLen))
expHead.SetBytes(getData(input, baseLen, expLen))
}
}