Fix review comments

Author: febo

scripts/setup/solana.dic

@@ -69,4 +69,4 @@ pinocchio
 mainnet
 getters
 PRNG
-middleware
+middleware

sdk/src/sysvars/rent.rs

@@ -51,21 +51,17 @@ pub const DEFAULT_LAMPORTS_PER_BYTE: u64 = 6960;
 )]
 pub const DEFAULT_EXEMPTION_THRESHOLD: f64 = 2.0;
 
-/// Default amount of time (in years) the balance has to include rent for the
-/// account to be rent exempt as a `u64`.
-const DEFAULT_EXEMPTION_THRESHOLD_AS_U64: u64 = 2;
-
 /// The `u64` representation of the default exemption threshold.
 ///
 /// This is used to check whether the `f64` value can be safely cast to a `u64`.
-const F64_EXEMPTION_THRESHOLD_AS_U64: u64 = 4611686018427387904;
+const CURRENT_EXEMPTION_THRESHOLD: [u8; 8] = [0, 0, 0, 0, 0, 0, 0, 64];
 
-/// The `u64` representation of the deprecated exemption threshold.
+/// The `f64::to_le_bytes` representation of the SIMD-0194 exemption threshold.
 ///
 /// This value is equivalent to `1f64`. It is only used to check whether
 /// the exemption threshold is the deprecated value to avoid performing
 /// floating-point operations on-chain.
-const F64_SIMD0194_EXEMPTION_THRESHOLD_AS_U64: u64 = 4607182418800017408;
+const SIMD0194_EXEMPTION_THRESHOLD: [u8; 8] = [0, 0, 0, 0, 0, 0, 240, 63];
 
 /// Default percentage of collected rent that is burned.
 ///
@@ -178,18 +174,16 @@ impl Rent {
     #[inline]
     pub fn minimum_balance(&self, data_len: usize) -> u64 {
         let bytes = data_len as u64;
-        let exemption_threshold_as_u64 = u64::from_le_bytes(self.exemption_threshold);
 
-        match exemption_threshold_as_u64 {
-            F64_SIMD0194_EXEMPTION_THRESHOLD_AS_U64 => {
+        match self.exemption_threshold {
+            SIMD0194_EXEMPTION_THRESHOLD => {
                 (ACCOUNT_STORAGE_OVERHEAD + bytes) * self.lamports_per_byte
             }
-            F64_EXEMPTION_THRESHOLD_AS_U64 => {
-                ((ACCOUNT_STORAGE_OVERHEAD + bytes) * self.lamports_per_byte)
-                    * DEFAULT_EXEMPTION_THRESHOLD_AS_U64
+            CURRENT_EXEMPTION_THRESHOLD => {
+                2 * (ACCOUNT_STORAGE_OVERHEAD + bytes) * self.lamports_per_byte
             }
             _ => {
-                #[cfg(any(target_os = "solana", not(target_arch = "bpf")))]
+                #[cfg(not(target_arch = "bpf"))]
                 {
                     (((ACCOUNT_STORAGE_OVERHEAD + bytes) * self.lamports_per_byte) as f64
                         * f64::from_le_bytes(self.exemption_threshold)) as u64
@@ -224,15 +218,15 @@ impl Sysvar for Rent {
 #[allow(deprecated)]
 mod tests {
     use crate::sysvars::rent::{
-        ACCOUNT_STORAGE_OVERHEAD, DEFAULT_BURN_PERCENT, DEFAULT_EXEMPTION_THRESHOLD,
-        DEFAULT_LAMPORTS_PER_BYTE, DEFAULT_LAMPORTS_PER_BYTE_YEAR,
+        ACCOUNT_STORAGE_OVERHEAD, CURRENT_EXEMPTION_THRESHOLD, DEFAULT_BURN_PERCENT,
+        DEFAULT_LAMPORTS_PER_BYTE, DEFAULT_LAMPORTS_PER_BYTE_YEAR, SIMD0194_EXEMPTION_THRESHOLD,
     };
 
     #[test]
     pub fn test_minimum_balance() {
         let mut rent = super::Rent {
             lamports_per_byte: DEFAULT_LAMPORTS_PER_BYTE_YEAR,
-            exemption_threshold: DEFAULT_EXEMPTION_THRESHOLD.to_le_bytes(),
+            exemption_threshold: CURRENT_EXEMPTION_THRESHOLD,
             burn_percent: DEFAULT_BURN_PERCENT,
         };
 
@@ -260,7 +254,7 @@ mod tests {
     pub fn test_minimum_balance_simd0194() {
         let mut rent = super::Rent {
             lamports_per_byte: DEFAULT_LAMPORTS_PER_BYTE,
-            exemption_threshold: 1.0f64.to_le_bytes(), // SIMD-0194 default
+            exemption_threshold: SIMD0194_EXEMPTION_THRESHOLD,
             burn_percent: DEFAULT_BURN_PERCENT,
         };