From dfde7ec43f4222896608aeb5cbbf2625a45db8da Mon Sep 17 00:00:00 2001
From: Christian Kamm <mail@ckamm.de>
Date: Wed, 11 Oct 2023 15:19:24 +0200
Subject: [PATCH] serum health: use lower-precision division (#750)

This saves around 1/3rd of the compute for active serum markets.
---
 programs/mango-v4/src/health/cache.rs                | 11 +++++++----
 programs/mango-v4/tests/cases/test_health_compute.rs |  4 ++--
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/programs/mango-v4/src/health/cache.rs b/programs/mango-v4/src/health/cache.rs
index 68f1eabbf..88aae888f 100644
--- a/programs/mango-v4/src/health/cache.rs
+++ b/programs/mango-v4/src/health/cache.rs
@@ -19,6 +19,7 @@ use anchor_lang::prelude::*;
 use fixed::types::I80F48;
 
 use crate::error::*;
+use crate::i80f48::LowPrecisionDivision;
 use crate::serum3_cpi::{OpenOrdersAmounts, OpenOrdersSlim};
 use crate::state::{
     Bank, MangoAccountRef, PerpMarket, PerpMarketIndex, PerpPosition, Serum3MarketIndex,
@@ -293,8 +294,9 @@ impl Serum3Info {
     ) -> I80F48 {
         let quote_asset = quote_info.prices.asset(health_type);
         let base_liab = base_info.prices.liab(health_type);
-        // OPTIMIZATION: These divisions can be extremely expensive (up to 5k CU each)
-        let reserved_quote_as_base_oracle = self.reserved_quote * quote_asset / base_liab;
+        let reserved_quote_as_base_oracle = (self.reserved_quote * quote_asset)
+            .checked_div_f64_precision(base_liab)
+            .unwrap();
         if self.reserved_quote_as_base_highest_bid != 0 {
             self.reserved_base
                 + reserved_quote_as_base_oracle.min(self.reserved_quote_as_base_highest_bid)
@@ -312,8 +314,9 @@ impl Serum3Info {
     ) -> I80F48 {
         let base_asset = base_info.prices.asset(health_type);
         let quote_liab = quote_info.prices.liab(health_type);
-        // OPTIMIZATION: These divisions can be extremely expensive (up to 5k CU each)
-        let reserved_base_as_quote_oracle = self.reserved_base * base_asset / quote_liab;
+        let reserved_base_as_quote_oracle = (self.reserved_base * base_asset)
+            .checked_div_f64_precision(quote_liab)
+            .unwrap();
         if self.reserved_base_as_quote_lowest_ask != 0 {
             self.reserved_quote
                 + reserved_base_as_quote_oracle.min(self.reserved_base_as_quote_lowest_ask)
diff --git a/programs/mango-v4/tests/cases/test_health_compute.rs b/programs/mango-v4/tests/cases/test_health_compute.rs
index 917b1de7c..f3d018adb 100644
--- a/programs/mango-v4/tests/cases/test_health_compute.rs
+++ b/programs/mango-v4/tests/cases/test_health_compute.rs
@@ -77,7 +77,7 @@ async fn test_health_compute_tokens() -> Result<(), TransportError> {
 #[tokio::test]
 async fn test_health_compute_serum() -> Result<(), TransportError> {
     let mut test_builder = TestContextBuilder::new();
-    test_builder.test().set_compute_max_units(150_000);
+    test_builder.test().set_compute_max_units(130_000);
     let context = test_builder.start_default().await;
     let solana = &context.solana.clone();
 
@@ -244,7 +244,7 @@ async fn test_health_compute_serum() -> Result<(), TransportError> {
     let avg_cu_increase = cu_measurements.windows(2).map(|p| p[1] - p[0]).sum::<u64>()
         / (cu_measurements.len() - 1) as u64;
     println!("average cu increase: {avg_cu_increase}");
-    assert!(avg_cu_increase < 10000);
+    assert!(avg_cu_increase < 7000);
 
     Ok(())
 }