fix: conversion of Ekubo x128 to Wad (#604)

This commit fixes a bug in the conversion of Ekubo's oracle
price to Wad. Unlike Ekubo Core, the Ekubo's oracle price
already returns the squared price.

Author: milancermak

src/core/receptor.cairo

@@ -9,7 +9,7 @@ pub mod receptor {
     use opus::interfaces::IReceptor::IReceptor;
     use opus::interfaces::IShrine::{IShrineDispatcher, IShrineDispatcherTrait};
     use opus::types::QuoteTokenInfo;
-    use opus::utils::math::{median_of_three, scale_x128_to_wad};
+    use opus::utils::math::{median_of_three, ekubo_oracle_price_to_wad};
     use starknet::{ContractAddress, get_block_timestamp};
     use wadray::{Wad, WAD_DECIMALS};
 
@@ -62,7 +62,7 @@ pub mod receptor {
     }
 
     //
-    // Events 
+    // Events
     //
 
     #[event]
@@ -166,7 +166,7 @@ pub mod receptor {
                 let quote_token_info: QuoteTokenInfo = self.quote_tokens.read(index);
                 let quote: u256 = oracle_extension
                     .get_price_x128_over_last(cash, quote_token_info.address, twap_duration);
-                let scaled_quote: Wad = scale_x128_to_wad(quote, quote_token_info.decimals);
+                let scaled_quote: Wad = ekubo_oracle_price_to_wad(quote, quote_token_info.decimals);
 
                 quotes.append(scaled_quote);
                 index += 1;

src/tests/receptor/test_receptor.cairo

@@ -236,9 +236,9 @@ mod test_receptor {
         // actual mainnet values from 1727418625 start time to 1727429425 end time
         // converted in python
         let prices: Span<u256> = array![
-            340309250276362099785975626643777172060, // 1.000158012403645039602034587 DAI / CASH
-            340527434977254803682969657, // 1.001440899252887204535902704 USDC / CASH
-            340328625112763872478829777, // 1.000271899695698999556601210 USDT / CASH
+            340309250276362099785975626643777172060, // 1.000079003081079 DAI / CASH
+            340527434977254803682969657, // 1.0007201902894171 USDC / CASH
+            340328625112763872478829777, // 1.000135940607925 USDT / CASH
         ]
             .span();
         receptor_utils::set_next_prices(
@@ -251,9 +251,9 @@ mod test_receptor {
         let quotes: Span<Wad> = receptor.get_quotes();
         let expected_yin_spot_price: Wad = *quotes[2];
         let mut expected_prices: Span<Wad> = array![
-            1000158012403645039_u128.into(), // DAI
-            1001440899252887204_u128.into(), // USDC
-            1000271899695698999_u128.into(), // USDT
+            1000079003081079000_u128.into(), // DAI
+            1000720190289417000_u128.into(), // USDC
+            1000135940607925000_u128.into(), // USDT
         ]
             .span();
         let error_margin: Wad = 200_u128.into();

src/tests/utils/test_math.cairo

@@ -2,7 +2,7 @@ mod test_math {
     use core::integer::BoundedInt;
     use core::num::traits::Zero;
     use opus::tests::common::assert_equalish;
-    use opus::utils::math::{median_of_three, pow, scale_x128_to_wad, sqrt};
+    use opus::utils::math::{median_of_three, pow, ekubo_oracle_price_to_wad, sqrt};
     use wadray::{Ray, RAY_ONE, Wad};
 
     #[test]
@@ -89,29 +89,29 @@ mod test_math {
     }
 
     #[test]
-    fn test_scale_x128_to_wad() {
+    fn test_ekubo_oracle_price_to_wad() {
         let error_margin: Wad = 200_u128.into();
 
         // 18 decimals
         let x128_val: u256 = 340351451218700252552422283729072753607;
-        let actual: Wad = scale_x128_to_wad(x128_val, 18);
-        let expected: Wad = 1000406082226072611_u128.into();
+        let actual: Wad = ekubo_oracle_price_to_wad(x128_val, 18);
+        let expected: Wad = 1000203020504373800_u128.into();
         assert_equalish(actual, expected, error_margin, 'wrong x128 to wad #1');
 
         let x128_val: u256 = 339351451218700252552422283729072753607;
-        let actual: Wad = scale_x128_to_wad(x128_val, 18);
-        let expected: Wad = 994536053393236430_u128.into();
+        let actual: Wad = ekubo_oracle_price_to_wad(x128_val, 18);
+        let expected: Wad = 997264284627318000_u128.into();
         assert_equalish(actual, expected, error_margin, 'wrong x128 to wad #2');
 
         // 6 decimals
         let x128_val: u256 = 340245254854570020996364378;
-        let actual: Wad = scale_x128_to_wad(x128_val, 6);
-        let expected: Wad = 999781886772824962_u128.into();
+        let actual: Wad = ekubo_oracle_price_to_wad(x128_val, 6);
+        let expected: Wad = 999890937439091300_u128.into();
         assert_equalish(actual, expected, error_margin, 'wrong x128 to wad #3');
 
         let x128_val: u256 = 341245254854570020996364378;
-        let actual: Wad = scale_x128_to_wad(x128_val, 6);
-        let expected: Wad = 1005667353683370322_u128.into();
+        let actual: Wad = ekubo_oracle_price_to_wad(x128_val, 6);
+        let expected: Wad = 1002829673316147100_u128.into();
         assert_equalish(actual, expected, error_margin, 'wrong x128 to wad #4');
     }
 

src/utils/math.cairo

@@ -47,22 +47,13 @@ pub fn div_u128_by_ray(lhs: u128, rhs: Ray) -> u128 {
 
 // If the quote token has less than 18 decimal precision, then the
 // x128 value needs to be scaled up by the quote token's decimals
-// https://docs.ekubo.org/integration-guides/reference/reading-pool-price
-pub fn scale_x128_to_wad(n: u256, decimals: u8) -> Wad {
-    let decimals_diff: u8 = WAD_DECIMALS - decimals;
-
-    // Scale value up to Wad precision first to avoid precision loss during division
-    let wad_scale: u256 = WAD_SCALE.into();
-    let scaled: u256 = n * wad_scale * pow(10, decimals_diff).into();
-    let sqrt: u256 = scaled / TWO_POW_128.into();
-
-    // `sqrt` is of Wad precision here so the result will be of 10 ** 36 precision
-    let sq: u512 = u256_wide_mul(sqrt, sqrt);
-
-    // Scale the value back to Wad precision
-    let (val, _) = u512_safe_div_rem_by_u256(sq, wad_scale.try_into().unwrap());
-
-    let val: u256 = val.try_into().unwrap();
+// See https://docs.ekubo.org/integration-guides/reference/reading-pool-price
+// for conversion of x128 values from the Ekubo Core. However, take note that 
+// Ekubo oracle extension already gives the squared price.
+pub fn ekubo_oracle_price_to_wad(n: u256, decimals: u8) -> Wad {
+    // we multiply by WAD_SCALE to get it into Wad precision and then mul again
+    // by the appropriate precision, all before dividing to prevent precision loss
+    let val: u256 = n * WAD_SCALE.into() * pow(10, WAD_DECIMALS - decimals).into() / TWO_POW_128.into();
     val.try_into().unwrap()
 }