math.go

package keeper

import (
	"github.com/osmosis-labs/osmosis/osmomath"

	sdk "github.com/cosmos/cosmos-sdk/types"
)

// Don't EVER change after initializing
// TODO: Analyze choice here
var powPrecision, _ = sdk.NewDecFromStr("0.00000001")

// Singletons
var zero sdk.Dec = sdk.ZeroDec()
var one_half sdk.Dec = sdk.MustNewDecFromStr("0.5")
var one sdk.Dec = sdk.OneDec()
var two sdk.Dec = sdk.MustNewDecFromStr("2")

// calcSpotPrice returns the spot price of the pool
// This is the weight-adjusted balance of the tokens in the pool.
// so spot_price = (B_in / W_in) / (B_out / W_out)
func calcSpotPrice(
	tokenBalanceIn,
	tokenWeightIn,
	tokenBalanceOut,
	tokenWeightOut sdk.Dec,
) sdk.Dec {
	number := tokenBalanceIn.Quo(tokenWeightIn)
	denom := tokenBalanceOut.Quo(tokenWeightOut)
	ratio := number.Quo(denom)

	return ratio
}

// calcSpotPriceWithSwapFee returns the spot price of the pool accounting for
// the input taken by the swap fee.
// This is the weight-adjusted balance of the tokens in the pool.
// so spot_price = (B_in / W_in) / (B_out / W_out)
// and spot_price_with_fee = spot_price / (1 - swapfee)
func calcSpotPriceWithSwapFee(
	tokenBalanceIn,
	tokenWeightIn,
	tokenBalanceOut,
	tokenWeightOut,
	swapFee sdk.Dec,
) sdk.Dec {
	spotPrice := calcSpotPrice(tokenBalanceIn, tokenWeightIn, tokenBalanceOut, tokenWeightOut)
	// Q: Why is this not just (1 - swapfee)
	// A: Its because its being applied to the other asset.
	// TODO: write this up more coherently
	// 1 / (1 - swapfee)
	scale := sdk.OneDec().Quo(sdk.OneDec().Sub(swapFee))

	return spotPrice.Mul(scale)
}

// aO
func calcOutGivenIn(
	tokenBalanceIn,
	tokenWeightIn,
	tokenBalanceOut,
	tokenWeightOut,
	tokenAmountIn,
	swapFee sdk.Dec,
) sdk.Dec {
	weightRatio := tokenWeightIn.Quo(tokenWeightOut)
	adjustedIn := sdk.OneDec().Sub(swapFee)
	adjustedIn = tokenAmountIn.Mul(adjustedIn)
	y := tokenBalanceIn.Quo(tokenBalanceIn.Add(adjustedIn))
	foo := osmomath.Pow(y, weightRatio)