make Shell Writer work.

src/shell.zig

@@ -6,25 +6,47 @@ const StringHashMap = std.StringHashMap;
 const BoundedArray = std.BoundedArray;
 const testing = std.testing;
 
+// MaxShells is the maximum number of "popular" shells.
+const MaxShells = 63;
+const MaxShellLen = 64;
+
 // ShellIndex is an index to the shell strings. As shell can be up to 64 bytes
 // (1<<6), maximum number of shells is 63 (1<<6-1), the maximum location offset
 // is 1<<12. To make location resolvable in 10 bits, all shells will be padded
 // to 4 bytes.
+// The actual shell length is len+1: we don't allow empty shells, and the real
+// length of the shell is 1-64 bytes.
 const ShellIndex = struct {
     offset: u10,
     len: u6,
 };
 
-// MaxShells is the maximum number of "popular" shells.
-const MaxShells = 63;
-const MaxShellLen = 64;
+// ShellReader interprets "Shell Index" and "Shell Blob" sections.
+const ShellReader = struct {
+    sectionIndex: []const ShellIndex,
+    sectionBlob: []const u8,
 
-// ShellPopcon is a shell popularity contest: collect shells and return the
+    pub fn init(index: []const u8, blob: []const u8) ShellReader {
+        return ShellReader{
+            .sectionIndex = @bitCast([]const ShellIndex, index),
+            .sectionBlob = blob,
+        };
+    }
+
+    // get returns a shell at the given index.
+    pub fn get(self: *ShellReader, idx: u10) []const u8 {
+        const shellIndex = self.sectionIndex[idx];
+        const start = shellIndex.offset << 2;
+        const end = start + shellIndex.len + 1;
+        return self.sectionBlob[start..end];
+    }
+};
+
+// ShellWriter is a shell popularity contest: collect shells and return the
 // popular ones, sorted by score. score := len(shell) * number_of_shells.
-const ShellPopcon = struct {
+const ShellWriter = struct {
     counts: std.StringHashMap(u32),
     allocator: Allocator,
-    const Self = @This();
     const KV = struct { shell: []const u8, score: u32 };
 
     const ShellSections = struct {
@@ -52,18 +74,28 @@ const ShellPopcon = struct {
                 try self.indices.put(ourShell, idx);
                 self.index.set(idx, ShellIndex{
                     .offset = @intCast(u10, fullOffset >> 2),
-                    .len = len,
+                    .len = len - 1,
                 });
 
-                // Padd padding to make offset divisible by 4.
-                const padding = (fullOffset + 3) & ~@intCast(u12, 3);
-                fullOffset += len + padding;
+                fullOffset += len;
+                const padding = roundUp4Padding(fullOffset);
+                fullOffset += padding;
+                //const stderr = std.io.getStdErr().writer();
+                //try stderr.print("\n", .{});
                 try self.blob.appendNTimes(0, padding);
                 idx += 1;
             }
             return self;
         }
 
+        pub fn sectionIndex(self: *ShellSections) []const u8 {
+            return @bitCast([]const u8, self.index.constSlice());
+        }
+
+        pub fn sectionBlob(self: *ShellSections) []const u8 {
+            return self.blob.constSlice();
+        }
+
         pub fn deinit(self: *ShellSections) void {
             self.indices.deinit();
             self.* = undefined;
@@ -74,14 +106,14 @@ const ShellPopcon = struct {
         }
     };
 
-    pub fn init(allocator: Allocator) Self {
-        return Self{
+    pub fn init(allocator: Allocator) ShellWriter {
+        return ShellWriter{
             .counts = std.StringHashMap(u32).init(allocator),
             .allocator = allocator,
         };
     }
 
-    pub fn deinit(self: *Self) void {
+    pub fn deinit(self: *ShellWriter) void {
         var it = self.counts.keyIterator();
         while (it.next()) |key_ptr| {
             self.counts.allocator.free(key_ptr.*);
@@ -90,7 +122,7 @@ const ShellPopcon = struct {
         self.* = undefined;
     }
 
-    pub fn put(self: *Self, shell: []const u8) !void {
+    pub fn put(self: *ShellWriter, shell: []const u8) !void {
         // TODO getOrPutAdapted may be more elegant, not sure which
         // context to pass.
         if (self.counts.getPtr(shell)) |ptr| {
@@ -108,9 +140,9 @@ const ShellPopcon = struct {
     }
 
     // toOwnedSections returns the analyzed ShellSections. Resets the shell
-    // popularity contest. ShellSections memory is allocated by the ShellPopcon
+    // popularity contest. ShellSections memory is allocated by the ShellWriter
     // allocator, and must be deInit'ed by the caller.
-    pub fn toOwnedSections(self: *Self, limit: u10) !ShellSections {
+    pub fn toOwnedSections(self: *ShellWriter, limit: u10) !ShellSections {
         var deque = PriorityDequeue(KV, void, cmpShells).init(self.allocator, {});
         defer deque.deinit();
 
@@ -141,8 +173,14 @@ const ShellPopcon = struct {
     }
 };
 
+// rounds up a u12 to the nearest factor of 4 and returns the difference
+// (padding)
+inline fn roundUp4Padding(n: u12) u12 {
+    return ((n + 3) & ~@intCast(u12, 3)) - n;
+}
+
 test "basic shellpopcon" {
-    var popcon = ShellPopcon.init(testing.allocator);
+    var popcon = ShellWriter.init(testing.allocator);
     defer popcon.deinit();
 
     const bash = "/bin/bash"; // 9 chars
@@ -163,21 +201,39 @@ test "basic shellpopcon" {
     defer sections.deinit();
     try testing.expectEqual(sections.index.len, 3); // all but "nobody" qualify
 
-    // TODO(motiejus): reverse the arguments: first should be "expected".
     try testing.expectEqual(sections.getIndex(long).?, 0);
     try testing.expectEqual(sections.getIndex(zsh).?, 1);
     try testing.expectEqual(sections.getIndex(bash).?, 2);
     try testing.expectEqual(sections.getIndex(nobody), null);
 
-    const idx = sections.getIndex(zsh).?;
-    const start = sections.index.get(idx).offset << 2;
-    const end = start + sections.index.get(idx).len;
-    const got = sections.blob.constSlice()[start..end];
+    var shellReader = ShellReader.init(
+        sections.sectionIndex(),
+        sections.sectionBlob(),
+    );
+    try testing.expectEqualStrings(shellReader.get(0), long);
+    try testing.expectEqualStrings(shellReader.get(1), zsh);
+    try testing.expectEqualStrings(shellReader.get(2), bash);
 
-    const stderr = std.io.getStdErr().writer();
-    try stderr.print("\n", .{});
-
-    try stderr.print("gotLong: {s}\n", .{got});
-    try stderr.print("   long: {s}\n", .{zsh});
-    try testing.expectEqual(got, zsh);
+    for ([_][]const u8{ long, zsh, bash }) |shell| {
+        const idx = sections.getIndex(shell).?;
+        const start = sections.index.get(idx).offset << 2;
+        const end = start + sections.index.get(idx).len + 1;
+        const got = sections.blob.constSlice()[start..end];
+        try testing.expectEqualStrings(got, shell);
+    }
+}
+
+test "padding" {
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 0)), 0);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 1)), 3);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 2)), 2);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 3)), 1);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 4)), 0);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 40)), 0);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 41)), 3);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 42)), 2);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 43)), 1);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 44)), 0);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 4091)), 1);
+    try testing.expectEqual(roundUp4Padding(@intCast(u12, 4092)), 0);
 }

src/test_main.zig

@@ -1,4 +1,4 @@
 test "turbonss test suite" {
     _ = @import("main.zig");
-    _ = @import("shellpop.zig");
+    _ = @import("shell.zig");
 }