argon2: move segment length calculation to Memory type (#159)

Begins the work of moving calculations about the memory buffer to the
`Memory` type.

argon2/src/instance.rs

@@ -52,9 +52,6 @@ pub(crate) struct Instance<'a> {
     /// Number of passes
     passes: u32,
 
-    /// Segment length
-    segment_length: u32,
-
     /// Lane length
     lane_length: u32,
 
@@ -97,12 +94,13 @@ impl<'a> Instance<'a> {
         mut initial_hash: digest::Output<Blake2b>,
         memory: Memory<'a>,
     ) -> Result<Self, Error> {
+        let lane_length = memory.segment_length() * SYNC_POINTS;
+
         let mut instance = Instance {
             version: context.version,
             memory,
             passes: context.t_cost,
-            segment_length: context.segment_length(),
-            lane_length: context.segment_length() * SYNC_POINTS,
+            lane_length,
             lanes: context.lanes,
             threads: context.threads,
             alg,
@@ -272,7 +270,7 @@ impl<'a> Instance<'a> {
 
         // Offset of the current block
         let mut curr_offset = position.lane * self.lane_length
-            + position.slice * self.segment_length
+            + position.slice * self.memory.segment_length()
             + starting_index;
 
         let mut prev_offset = if 0 == curr_offset % self.lane_length {
@@ -283,7 +281,7 @@ impl<'a> Instance<'a> {
             curr_offset - 1
         };
 
-        for i in starting_index..self.segment_length {
+        for i in starting_index..self.memory.segment_length() {
             // 1.1 Rotating prev_offset if needed
             if curr_offset % self.lane_length == 1 {
                 prev_offset = curr_offset - 1;
@@ -361,16 +359,19 @@ impl<'a> Instance<'a> {
                 position.index - 1 // all but the previous
             } else if same_lane {
                 // The same lane => add current segment
-                position.slice * self.segment_length + position.index - 1
+                position.slice * self.memory.segment_length() + position.index - 1
             } else {
-                position.slice * self.segment_length - if position.index == 0 { 1 } else { 0 }
+                position.slice * self.memory.segment_length()
+                    - if position.index == 0 { 1 } else { 0 }
             }
         } else {
             // Second pass
             if same_lane {
-                self.lane_length - self.segment_length + position.index - 1
+                self.lane_length - self.memory.segment_length() + position.index - 1
             } else {
-                self.lane_length - self.segment_length - if position.index == 0 { 1 } else { 0 }
+                self.lane_length
+                    - self.memory.segment_length()
+                    - if position.index == 0 { 1 } else { 0 }
             }
         };
 
@@ -389,7 +390,7 @@ impl<'a> Instance<'a> {
             start_position = if position.slice == SYNC_POINTS - 1 {
                 0
             } else {
-                (position.slice + 1) * self.segment_length
+                (position.slice + 1) * self.memory.segment_length()
             }
         }
 

argon2/src/lib.rs

@@ -87,7 +87,11 @@ pub use crate::error::Error;
 #[cfg_attr(docsrs, doc(cfg(feature = "password-hash")))]
 pub use password_hash::{self, PasswordHash, PasswordHasher, PasswordVerifier};
 
-use crate::{block::Block, instance::Instance, memory::Memory};
+use crate::{
+    block::Block,
+    instance::Instance,
+    memory::{Memory, SYNC_POINTS},
+};
 use blake2::{digest, Blake2b, Digest};
 use core::{
     convert::TryFrom,
@@ -149,9 +153,6 @@ pub const MAX_SECRET: usize = 0xFFFFFFFF;
 /// Memory block size in bytes
 pub const BLOCK_SIZE: usize = 1024;
 
-/// Number of synchronization points between lanes per pass
-const SYNC_POINTS: u32 = 4;
-
 /// Argon2d algorithm identifier
 #[cfg(feature = "password-hash")]
 #[cfg_attr(docsrs, doc(cfg(feature = "password-hash")))]
@@ -478,15 +479,17 @@ impl<'key> Argon2<'key> {
             return Err(Error::AdTooLong);
         }
 
-        let memory_blocks = (self.segment_length() * self.lanes * SYNC_POINTS) as usize;
-
         // Hashing all inputs
         let initial_hash = self.initial_hash(alg, pwd, salt, ad, out);
 
+        let segment_length = Memory::segment_length_for_params(self.m_cost, self.lanes);
+        let blocks_count = (segment_length * self.lanes * SYNC_POINTS) as usize;
+
         // TODO(tarcieri): support for stack-allocated memory blocks (i.e. no alloc)
-        let mut memory = vec![Block::default(); memory_blocks];
+        let mut blocks = vec![Block::default(); blocks_count];
 
-        Instance::hash(self, alg, initial_hash, Memory::new(&mut memory), out)
+        let memory = Memory::new(&mut blocks, segment_length);
+        Instance::hash(self, alg, initial_hash, memory, out)
     }
 
     /// Hashes all the inputs into `blockhash[PREHASH_DIGEST_LENGTH]`.
@@ -521,18 +524,6 @@ impl<'key> Argon2<'key> {
         digest.update(ad);
         digest.finalize()
     }
-
-    pub(crate) fn segment_length(&self) -> u32 {
-        // Align memory size
-        // Minimum memory_blocks = 8L blocks, where L is the number of lanes
-        let memory_blocks = if self.m_cost < 2 * SYNC_POINTS * self.lanes {
-            2 * SYNC_POINTS * self.lanes
-        } else {
-            self.m_cost
-        };
-
-        memory_blocks / (self.lanes * SYNC_POINTS)
-    }
 }
 
 #[cfg(feature = "password-hash")]

argon2/src/memory.rs

@@ -2,21 +2,38 @@
 
 use crate::Block;
 
+/// Number of synchronization points between lanes per pass
+pub(crate) const SYNC_POINTS: u32 = 4;
+
 /// Structure containing references to the memory blocks
 pub(crate) struct Memory<'a> {
     /// Memory blocks
     data: &'a mut [Block],
 
-    /// Size of the memory in blocks
-    size: usize,
+    /// Size of a memory segment in blocks
+    segment_length: u32,
 }
 
 impl<'a> Memory<'a> {
-    /// Instantiate a new memory struct
-    pub(crate) fn new(data: &'a mut [Block]) -> Self {
-        let size = data.len();
+    /// Align memory size.
+    ///
+    /// Minimum memory_blocks = 8*`L` blocks, where `L` is the number of lanes.
+    pub(crate) fn segment_length_for_params(m_cost: u32, lanes: u32) -> u32 {
+        let memory_blocks = if m_cost < 2 * SYNC_POINTS * lanes {
+            2 * SYNC_POINTS * lanes
+        } else {
+            m_cost
+        };
+
+        memory_blocks / (lanes * SYNC_POINTS)
+    }
 
-        Self { data, size }
+    /// Instantiate a new memory struct
+    pub(crate) fn new(data: &'a mut [Block], segment_length: u32) -> Self {
+        Self {
+            data,
+            segment_length,
+        }
     }
 
     /// Get a copy of the block
@@ -30,7 +47,14 @@ impl<'a> Memory<'a> {
     }
 
     /// Size of the memory
+    #[inline]
     pub(crate) fn len(&self) -> usize {
-        self.size
+        self.data.len()
+    }
+
+    /// Size of a memory segment
+    #[inline]
+    pub(crate) fn segment_length(&self) -> u32 {
+        self.segment_length
     }
 }