Commit 9f215318b8967940a8fc2385de9bc0e3faf02e7e | zig

author	Jonathan Marler <johnnymarler@gmail.com> 2022-11-16 23:41:54-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2023-01-09 14:18:01-07:00
log	9f215318b8967940a8fc2385de9bc0e3faf02e7e
tree	d084f0db90dcb4744cc70325a0dbc5ae8b836b05
parent	91b8d9e370f0dfc62f7bf7297ce9a7e22bae9f67

packed struct fix example and clarify least to most significant ordering

The packed struct example was mistakenly applying endianness where it
shouldn't have been.  This wasn't being caught because we don't currently
test the examples on Big-endian systems.

I updated the test to remove the endianness where it didn't apply, and
added a new part of the test to demonstrate when it would apply.

1 files changed, 10 insertions(+), 7 deletions(-)

doc
- langref.html.in

doc/langref.html.in+10-7

 @@ -3277,7 +3277,7 @@ test "default struct initialization fields" {
       Unlike normal structs, {#syntax#}packed{#endsyntax#} structs have guaranteed in-memory layout:
       </p>
       <ul>
-        <li>Fields remain in the order declared.</li>
+        <li>Fields remain in the order declared, least to most significant.</li>
         <li>There is no padding between fields.</li>
         <li>Zig supports arbitrary width {#link|Integers#} and although normally, integers with fewer
         than 8 bits will still use 1 byte of memory, in packed structs, they use
 @@ -3320,16 +3320,19 @@ fn doTheTest() !void {
     try expect(@sizeOf(Divided) == 2);
     var full = Full{ .number = 0x1234 };
     var divided = @bitCast(Divided, full);
+    try expect(divided.half1 == 0x34);
+    try expect(divided.quarter3 == 0x2);
+    try expect(divided.quarter4 == 0x1);
+    var ordered = @bitCast([2]u8, full);
     switch (native_endian) {
         .Big => {
-            try expect(divided.half1 == 0x12);
+            try expect(ordered[0] == 0x12);
-            try expect(divided.quarter3 == 0x3);
+            try expect(ordered[1] == 0x34);
-            try expect(divided.quarter4 == 0x4);
         },
         .Little => {
-            try expect(divided.half1 == 0x34);
+            try expect(ordered[0] == 0x34);
-            try expect(divided.quarter3 == 0x2);
+            try expect(ordered[1] == 0x12);
-            try expect(divided.quarter4 == 0x1);
         },
     }
 }