BREAKING: Use packed structs (#7)

#### Problem

Many of the structs in the SDK use `extern` layout. While this ensures
compatibility with C ABI, it can also be less performant for on-chain
programs.

#### Summary of changes

Move `PublicKey`, `Account.Data`, and `Rent` to be `packed` structs.
This is a breaking change because the underlying layout of many types
will change.

Author: joncinque

src/account.zig

@@ -4,29 +4,30 @@ const PublicKey = @import("public_key.zig").PublicKey;
 pub const ACCOUNT_DATA_PADDING = 10 * 1024;
 
 pub const Account = struct {
+    pub const DATA_HEADER = 88;
     /// A Solana account sliced from what is provided as inputs to the BPF virtual machine.
-    pub const Data = extern struct {
+    pub const Data = packed struct {
         duplicate_index: u8,
-        is_signer: bool,
-        is_writable: bool,
-        is_executable: bool,
-        _: [4]u8,
+        is_signer: u8,
+        is_writable: u8,
+        is_executable: u8,
+        original_data_len: u32,
         id: PublicKey,
         owner_id: PublicKey,
         lamports: u64,
-        data_len: usize,
+        data_len: u64,
 
         comptime {
             std.debug.assert(@offsetOf(Account.Data, "duplicate_index") == 0);
             std.debug.assert(@offsetOf(Account.Data, "is_signer") == 0 + 1);
             std.debug.assert(@offsetOf(Account.Data, "is_writable") == 0 + 1 + 1);
             std.debug.assert(@offsetOf(Account.Data, "is_executable") == 0 + 1 + 1 + 1);
-            std.debug.assert(@offsetOf(Account.Data, "_") == 0 + 1 + 1 + 1 + 1);
+            std.debug.assert(@offsetOf(Account.Data, "original_data_len") == 0 + 1 + 1 + 1 + 1);
             std.debug.assert(@offsetOf(Account.Data, "id") == 0 + 1 + 1 + 1 + 1 + 4);
             std.debug.assert(@offsetOf(Account.Data, "owner_id") == 0 + 1 + 1 + 1 + 1 + 4 + 32);
             std.debug.assert(@offsetOf(Account.Data, "lamports") == 0 + 1 + 1 + 1 + 1 + 4 + 32 + 32);
             std.debug.assert(@offsetOf(Account.Data, "data_len") == 0 + 1 + 1 + 1 + 1 + 4 + 32 + 32 + 8);
-            std.debug.assert(@sizeOf(Account.Data) == 1 + 1 + 1 + 1 + 4 + 32 + 32 + 8 + 8);
+            std.debug.assert(@bitSizeOf(Account.Data) == DATA_HEADER * 8);
         }
     };
 
@@ -63,30 +64,46 @@ pub const Account = struct {
         return self.ptr.owner_id;
     }
 
+    pub fn assign(self: Account, new_owner_id: PublicKey) void {
+        self.ptr.owner_id = new_owner_id;
+    }
+
     pub fn data(self: Account) []u8 {
-        const data_ptr = @as([*]u8, @ptrFromInt(@intFromPtr(self.ptr))) + @sizeOf(Account.Data);
+        const data_ptr = @as([*]u8, @ptrFromInt(@intFromPtr(self.ptr))) + DATA_HEADER;
         return data_ptr[0..self.ptr.data_len];
     }
 
     pub fn isWritable(self: Account) bool {
-        return self.ptr.is_writable;
+        return self.ptr.is_writable == 1;
     }
 
     pub fn isExecutable(self: Account) bool {
-        return self.ptr.is_executable;
+        return self.ptr.is_executable == 1;
     }
 
     pub fn isSigner(self: Account) bool {
-        return self.ptr.is_signer;
+        return self.ptr.is_signer == 1;
     }
 
-    pub fn dataLen(self: Account) usize {
+    pub fn dataLen(self: Account) u64 {
         return self.ptr.data_len;
     }
 
+    pub fn realloc(self: Account, new_data_len: u64) error.InvalidRealloc!void {
+        const diff = @subWithOverflow(new_data_len, self.original_data_len);
+        if (diff[1] == 0 and diff[0] > ACCOUNT_DATA_PADDING) {
+            return error.InvalidRealloc;
+        }
+        self.reallocUnchecked(new_data_len);
+    }
+
+    pub fn reallocUnchecked(self: Account, new_data_len: u64) void {
+        self.ptr.data_len = new_data_len;
+    }
+
     pub fn info(self: Account) Account.Info {
-        const data_ptr = @as([*]u8, @ptrFromInt(@intFromPtr(self.ptr))) + @sizeOf(Account.Data);
-        const rent_epoch = @as(*u64, @ptrFromInt(std.mem.alignForward(usize, @intFromPtr(self.ptr) + self.ptr.data_len + ACCOUNT_DATA_PADDING, @alignOf(usize))));
+        const data_ptr = @as([*]u8, @ptrFromInt(@intFromPtr(self.ptr))) + DATA_HEADER;
+        const rent_epoch = @as(*u64, @ptrFromInt(std.mem.alignForward(u64, @intFromPtr(self.ptr) + self.ptr.data_len + ACCOUNT_DATA_PADDING, @alignOf(u64))));
 
         return .{
             .id = &self.ptr.id,

src/context.zig

@@ -9,7 +9,7 @@ pub const Context = struct {
     num_accounts: usize,
     accounts: [64]Account,
     data: []const u8,
-    program_id: *PublicKey,
+    program_id: *align(1) PublicKey,
 
     pub fn load(input: [*]u8) !Context {
         var ptr: [*]u8 = input;
@@ -25,7 +25,7 @@ pub const Context = struct {
                 ptr += @sizeOf(usize);
                 accounts[i] = accounts[data.duplicate_index];
             } else {
-                ptr += @sizeOf(Account.Data);
+                ptr += Account.DATA_HEADER;
                 ptr = @as([*]u8, @ptrFromInt(std.mem.alignForward(usize, @intFromPtr(ptr) + data.data_len + ACCOUNT_DATA_PADDING, @alignOf(usize))));
                 ptr += @sizeOf(u64);
                 accounts[i] = .{ .ptr = @as(*Account.Data, @ptrCast(@alignCast(data))) };
@@ -39,7 +39,7 @@ pub const Context = struct {
         const data = ptr[0..data_len];
         ptr += data_len;
 
-        const program_id = @as(*PublicKey, @ptrCast(ptr));
+        const program_id = @as(*align(1) PublicKey, @ptrCast(ptr));
         ptr += @sizeOf(PublicKey);
 
         return Context{

src/public_key.zig

@@ -13,17 +13,17 @@ pub const ProgramDerivedAddress = struct {
     bump_seed: [1]u8,
 };
 
-pub const PublicKey = extern struct {
+pub const PublicKey = packed struct {
     pub const length: usize = 32;
     pub const base58_length: usize = 44;
 
     pub const max_num_seeds: usize = 16;
     pub const max_seed_length: usize = 32;
 
-    bytes: [PublicKey.length]u8,
+    bytes: u256,
 
     pub fn from(bytes: [PublicKey.length]u8) PublicKey {
-        return .{ .bytes = bytes };
+        return .{ .bytes = mem.bytesToValue(u256, &bytes) };
     }
 
     pub fn comptimeFromBase58(comptime encoded: []const u8) PublicKey {
@@ -47,11 +47,11 @@ pub const PublicKey = extern struct {
     }
 
     pub fn equals(self: PublicKey, other: PublicKey) bool {
-        return mem.eql(u8, &self.bytes, &other.bytes);
+        return self.bytes == other.bytes;
     }
 
     pub fn isPointOnCurve(self: PublicKey) bool {
-        const Y = std.crypto.ecc.Curve25519.Fe.fromBytes(self.bytes);
+        const Y = std.crypto.ecc.Curve25519.Fe.fromBytes(mem.toBytes(self.bytes));
         const Z = std.crypto.ecc.Curve25519.Fe.one;
         const YY = Y.sq();
         const u = YY.sub(Z);
@@ -125,9 +125,9 @@ pub const PublicKey = extern struct {
         inline while (i < seeds.len) : (i += 1) {
             hasher.update(seeds[i]);
         }
-        hasher.update(&program_id.bytes);
+        hasher.update(mem.asBytes(&program_id.bytes));
         hasher.update("ProgramDerivedAddress");
-        hasher.final(&address.bytes);
+        hasher.final(mem.asBytes(&address.bytes));
 
         if (address.isPointOnCurve()) {
             return error.InvalidSeeds;
@@ -222,7 +222,7 @@ pub const PublicKey = extern struct {
         _ = fmt;
         _ = options;
         var buffer: [base58.bitcoin.getEncodedLengthUpperBound(PublicKey.length)]u8 = undefined;
-        try writer.print("{s}", .{base58.bitcoin.encode(&buffer, &self.bytes)});
+        try writer.print("{s}", .{base58.bitcoin.encode(&buffer, mem.asBytes(&self.bytes))});
     }
 };
 

src/rent.zig

@@ -21,7 +21,7 @@ pub const Rent = struct {
     /// Account storage overhead for calculation of base rent.
     pub const account_storage_overhead: u64 = 128;
 
-    pub const Data = extern struct {
+    pub const Data = packed struct {
         lamports_per_byte_year: u64 = Rent.default_lamports_per_byte_year,
         exemption_threshold: f64 = Rent.default_exemption_threshold,
         burn_percent: u8 = Rent.default_burn_percent,
@@ -43,7 +43,7 @@ pub const Rent = struct {
 
         pub fn getMinimumBalance(self: Rent.Data, data_len: usize) u64 {
             const total_data_len: u64 = Rent.account_storage_overhead + data_len;
-            return @intFromFloat(@as(f64, @floatFromInt(total_data_len * self.lamports_per_byte_year)) * self.exemption_threshold);
+            return total_data_len * self.lamports_per_byte_year * @as(u64, @intFromFloat(self.exemption_threshold));
         }
     };