From 80ec63b6a422392936ef6b9630baed55452b5df1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Motiejus=20Jak=C5=A1tys?= <motiejus@jakstys.lt>
Date: Fri, 18 Feb 2022 15:25:10 +0200
Subject: [PATCH] fix casting functions, add some tests

---
 src/header.zig |  9 ++++++---
 src/shell.zig  | 24 ++++++++++++------------
 2 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/src/header.zig b/src/header.zig
index bfff6c7..ea55359 100644
--- a/src/header.zig
+++ b/src/header.zig
@@ -6,6 +6,8 @@ const Magic = [4]u8{ 0xf0, 0x9f, 0xa4, 0xb7 };
 const Version = 0;
 const Bom = 0x1234;
 
+pub const SectionLength = 64;
+
 const HeaderError = error{
     InvalidMagic,
     InvalidVersion,
@@ -56,7 +58,7 @@ const Header = packed struct {
             self.offset_additional_gids,
         };
         for (offsets) |offset| {
-            if (offset & @intCast(u32, 63) != 0) {
+            if (offset & (SectionLength - 1) != 0) {
                 return error.InvalidOffset;
             }
         }
@@ -71,8 +73,9 @@ const Header = packed struct {
 
 const testing = std.testing;
 
-test "header size is byte-aligned" {
+test "constants and types are reasonable" {
     try testing.expectEqual(HeaderSize * 8, @bitSizeOf(Header));
+    try testing.expect(std.math.isPowerOfTwo(SectionLength));
 }
 
 test "header pack and unpack" {
@@ -117,7 +120,7 @@ test "header pack and unpack" {
 
     {
         var header = goodHeader;
-        header.offset_cmph_uid2user = 128;
+        header.offset_cmph_uid2user = 65;
         try testing.expectError(error.InvalidOffset, Header.init(header.asArray()));
     }
 }
diff --git a/src/shell.zig b/src/shell.zig
index cd0a279..2d1c5b8 100644
--- a/src/shell.zig
+++ b/src/shell.zig
@@ -10,17 +10,6 @@ const StringContext = std.hash_map.StringContext;
 pub const MaxShells = 63;
 pub 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,
-};
-
 // ShellReader interprets "Shell Index" and "Shell Blob" sections.
 pub const ShellReader = struct {
     sectionIndex: []const ShellIndex,
@@ -81,7 +70,7 @@ pub const ShellWriter = struct {
                 const padding = roundUp4Padding(fullOffset);
                 fullOffset += padding;
                 //const stderr = std.io.getStdErr().writer();
-                //try stderr.print("\n", .{});
+                //stderr.print("\n", .{}) catch unreachable;
                 try self.blob.appendNTimes(0, padding);
                 idx += 1;
             }
@@ -181,6 +170,17 @@ inline fn roundUp4Padding(n: u12) u12 {
     return ((n + 3) & ~@intCast(u12, 3)) - n;
 }
 
+// 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,
+};
+
 const testing = std.testing;
 
 test "basic shellpopcon" {