codec - universal_decode_number optimziation

data/codec/src/impl_for_types/impl_num_signed.rs

@@ -1,7 +1,7 @@
 use crate::{
-    dep_encode_num_mimic, num_conv::universal_decode_number, DecodeError, DecodeErrorHandler,
-    EncodeErrorHandler, NestedDecode, NestedDecodeInput, NestedEncode, NestedEncodeOutput,
-    TopDecode, TopDecodeInput, TopEncode, TopEncodeOutput,
+    dep_encode_num_mimic, num_conv::universal_decode_number_unchecked, DecodeError,
+    DecodeErrorHandler, EncodeErrorHandler, NestedDecode, NestedDecodeInput, NestedEncode,
+    NestedEncodeOutput, TopDecode, TopDecodeInput, TopEncode, TopEncodeOutput,
 };
 
 macro_rules! top_encode_num_signed {
@@ -42,7 +42,7 @@ macro_rules! dep_decode_num_signed {
             {
                 let mut bytes = [0u8; $num_bytes];
                 input.read_into(&mut bytes[..], h)?;
-                let num = universal_decode_number(&bytes[..], true) as $ty;
+                let num = universal_decode_number_unchecked(&bytes[..], true) as $ty;
                 Ok(num)
             }
         }

data/codec/src/impl_for_types/impl_num_unsigned.rs

@@ -1,7 +1,7 @@
 use crate::{
-    dep_encode_num_mimic, num_conv::universal_decode_number, DecodeError, DecodeErrorHandler,
-    EncodeErrorHandler, NestedDecode, NestedDecodeInput, NestedEncode, NestedEncodeOutput,
-    TopDecode, TopDecodeInput, TopEncode, TopEncodeOutput,
+    dep_encode_num_mimic, num_conv::universal_decode_number_unchecked, DecodeError,
+    DecodeErrorHandler, EncodeErrorHandler, NestedDecode, NestedDecodeInput, NestedEncode,
+    NestedEncodeOutput, TopDecode, TopDecodeInput, TopEncode, TopEncodeOutput,
 };
 
 // No reversing needed for u8, because it is a single byte.
@@ -102,7 +102,7 @@ macro_rules! dep_decode_num_unsigned {
             {
                 let mut bytes = [0u8; $num_bytes];
                 input.read_into(&mut bytes[..], h)?;
-                let num = universal_decode_number(&bytes[..], false) as $ty;
+                let num = universal_decode_number_unchecked(&bytes[..], false) as $ty;
                 Ok(num)
             }
         }

data/codec/src/num_conv.rs

@@ -110,23 +110,32 @@ fn fill_buffer_find_offset(x: u64, signed: bool, buffer: &mut TopEncodeNumberBuf
 ///
 /// No generics here, we avoid monomorphization to make the SC binary as small as possible.
 pub fn universal_decode_number(bytes: &[u8], signed: bool) -> u64 {
-    if bytes.is_empty() {
-        return 0;
-    }
-    let negative = signed && msbit_is_one(bytes[0]);
-    let mut result = if negative {
-        // start with all bits set to 1,
-        // to ensure that if there are fewer bytes than the result type width,
-        // the leading bits will be 1 instead of 0
-        u64::MAX
-    } else {
-        0u64
-    };
-    for byte in bytes.iter() {
-        result <<= 8;
-        result |= *byte as u64;
+    // it is almost impossible to get a slice longer than 8
+    // just a basic overflow/underflow protection
+    let safe_len = bytes.len() % 9;
+    universal_decode_number_impl(bytes, safe_len, signed)
+}
+
+/// Same as [`universal_decode_number`], but assumes that the input length does not exceed 8.
+pub fn universal_decode_number_unchecked(bytes: &[u8], signed: bool) -> u64 {
+    universal_decode_number_impl(bytes, bytes.len(), signed)
+}
+
+fn universal_decode_number_impl(bytes: &[u8], len: usize, signed: bool) -> u64 {
+    let negative = signed && len > 0 && msbit_is_one(bytes[0]);
+    let skippable_byte = skippable_byte(negative);
+
+    let mut extended_buffer = [skippable_byte; 8];
+    let offset = 8 - len;
+    unsafe {
+        core::ptr::copy_nonoverlapping(
+            bytes.as_ptr(),
+            extended_buffer.as_mut_ptr().add(offset),
+            len,
+        )
     }
-    result
+
+    u64::from_be_bytes(extended_buffer)
 }
 
 /// Most significant bit is 1.

data/codec/src/single/top_de_input.rs

@@ -1,6 +1,7 @@
 use crate::{
-    num_conv::universal_decode_number, transmute::vec_into_boxed_slice, DecodeError,
-    DecodeErrorHandler, NestedDecodeInput, OwnedBytesNestedDecodeInput, TryStaticCast,
+    num_conv::{universal_decode_number, universal_decode_number_unchecked},
+    transmute::vec_into_boxed_slice,
+    DecodeError, DecodeErrorHandler, NestedDecodeInput, OwnedBytesNestedDecodeInput, TryStaticCast,
 };
 use alloc::{boxed::Box, vec::Vec};
 
@@ -38,7 +39,7 @@ pub trait TopDecodeInput: Sized {
     {
         let mut buffer = [0u8; 8];
         let slice = self.into_max_size_buffer(&mut buffer, h)?;
-        Ok(universal_decode_number(slice, false))
+        Ok(universal_decode_number_unchecked(slice, false))
     }
 
     /// Retrieves the underlying data as a pre-parsed i64.
@@ -51,7 +52,7 @@ pub trait TopDecodeInput: Sized {
     {
         let mut buffer = [0u8; 8];
         let slice = self.into_max_size_buffer(&mut buffer, h)?;
-        Ok(universal_decode_number(slice, true) as i64)
+        Ok(universal_decode_number_unchecked(slice, true) as i64)
     }
 
     #[inline]

data/codec/tests/derive_hygiene.rs

@@ -35,6 +35,7 @@ use crate::Result::{Err, Ok};
 // They are not used in the derive, but just to make sure:
 fn top_encode_number() {}
 fn universal_decode_number() {}
+fn universal_decode_number_unchecked() {}
 fn dep_decode_from_byte_slice() {}
 fn dep_encode_to_vec() {}
 fn top_decode_from_nested_or_handle_err() {}