comments and test

Signed-off-by: microwavedcola1 <microwavedcola@gmail.com>

programs/mango-v4/src/instructions/liq_token_with_token.rs

@@ -83,6 +83,7 @@ pub fn liq_token_with_token(
             .native(&liab_bank);
         require!(liqee_liab_native.is_negative(), MangoError::SomeError);
 
+        // TODO why sum of both tokens liquidation fees? Add comment
         let fee_factor = I80F48::ONE + asset_bank.liquidation_fee + liab_bank.liquidation_fee;
         let liab_price_adjusted = liab_price * fee_factor;
 

programs/mango-v4/src/state/health.rs

@@ -145,6 +145,12 @@ impl<'a, 'b> AccountRetriever<'a, 'b> for ScanningAccountRetriever<'a, 'b> {
     }
 }
 
+/// There are two types of health, initial health used for opening new positions and maintenance
+/// health used for liquidations. They are both calculated as a weighted sum of the assets
+/// minus the liabilities but the maint. health uses slightly larger weights for assets and
+/// slightly smaller weights for the liabilities. Zero is used as the bright line for both
+/// i.e. if your init health falls below zero, you cannot open new positions and if your maint. health
+/// falls below zero you will be liquidated.
 #[derive(PartialEq, Copy, Clone)]
 pub enum HealthType {
     Init,
@@ -368,3 +374,33 @@ fn compute_health_detail<'a, 'b: 'a>(
 
     Ok(HealthCache { token_infos })
 }
+
+#[cfg(test)]
+mod tests {
+    use std::str::FromStr;
+
+    use fixed::types::I80F48;
+
+    #[test]
+    fn test_precision() {
+        // I80F48 can only represent until 1/2^48
+        assert_ne!(
+            I80F48::from_num(1_u128) / I80F48::from_num(2_u128.pow(48)),
+            0
+        );
+        assert_eq!(
+            I80F48::from_num(1_u128) / I80F48::from_num(2_u128.pow(49)),
+            0
+        );
+
+        // I80F48 can only represent until 14 decimal points
+        assert_ne!(
+            I80F48::from_str(format!("0.{}1", "0".repeat(13)).as_str()).unwrap(),
+            0
+        );
+        assert_eq!(
+            I80F48::from_str(format!("0.{}1", "0".repeat(14)).as_str()).unwrap(),
+            0
+        );
+    }
+}