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std.debug.dump_hex address on partial line incorrect #20048

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Khitiara opened this issue May 23, 2024 · 4 comments · Fixed by #23300
Closed

std.debug.dump_hex address on partial line incorrect #20048

Khitiara opened this issue May 23, 2024 · 4 comments · Fixed by #23300
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bug Observed behavior contradicts documented or intended behavior standard library This issue involves writing Zig code for the standard library.
Milestone
0.16.0

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@Khitiara
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Zig Version

0.13.0-dev.245+5fe9f88b1

Steps to Reproduce and Observed Behavior

replication source and zig run output:
https://gist.github.com/Khitiara/ce35b7ba82304a8d540cda822512454e

Expected Behavior

expected output also provided along with a possible fix in the above gist, the important line being on line 18:

-        const address = (@intFromPtr(bytes.ptr) + 0x10 * (chunks.index orelse 0) / 16) - 0x10;
+        const address = (@intFromPtr(bytes.ptr) + 0x10 * (try std.math.divCeil(usize, chunks.index orelse bytes.len, 16))) - 0x10;
@Khitiara Khitiara added the bug Observed behavior contradicts documented or intended behavior label May 23, 2024
@Arnau478
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About the potential fix: I think the divCeil call should have a catch unreachable instead of a try. This is because divCeil can only fail when the denominator is zero (obviously) or between 1 and -1 (it could overflow). 16 cannot cause an error.

Arnau478 added a commit to Arnau478/zig that referenced this issue May 23, 2024
@Arnau478
Fix bug in std.debug.dump_hex
3a55f8e 
Fixes ziglang#20048
@Arnau478 Arnau478 mentioned this issue May 23, 2024
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@squeek502
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Just want to note that std.testing.expectEqualSlices doesn't exhibit this bug (dump_hex and expectEqualSlices don't share implementations):

const std = @import("std");

test {
    const bytes: []const u8 = &.{ 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, 0x01, 0x12, 0x13 };
    try std.testing.expectEqualSlices(u8, bytes, "");
}
Test [1/1] dump_hex.test_0... slices differ. first difference occurs at index 0 (0x0)

============ expected this output: =============  len: 19 (0x13)

00 11 22 33 44 55 66 77  88 99 AA BB CC DD EE FF  .."3DUfw........
01 12 13                                          ...

============= instead found this: ==============  len: 0 (0x0)



================================================

@Khitiara
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@squeek502 note that the std.testing function does not report the address of each 16-byte line which is where the bug is in std.debug.dump_hex

@squeek502
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squeek502 commented May 23, 2024 •
edited
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Oh, I was looking at the wrong thing. I saw the missing ... on the bottom line of the ouput.txt and thought that was the problem. Ignore me then

@Vexu Vexu added the standard library This issue involves writing Zig code for the standard library. label May 24, 2024
@Vexu Vexu added this to the 0.14.0 milestone May 24, 2024
@andrewrk andrewrk modified the milestones: 0.14.0, 0.16.0 Feb 9, 2025
Arnau478 added a commit to Arnau478/zig that referenced this issue Mar 19, 2025
@Arnau478
Fix std.debug.dumpHex address offsets
6aebed5 
Abstracts the logic to std.debug.dumpHexInternal, which takes a writer
and TTY config. That way, unit tests can be written for the function.

Fixes ziglang#20048
@Arnau478 Arnau478 mentioned this issue Mar 19, 2025
Merged
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bug Observed behavior contradicts documented or intended behavior standard library This issue involves writing Zig code for the standard library.
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0.16.0
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Fix std.debug.dumpHex address offsets Arnau478/zig
Fix bug in std.debug.dump_hex Arnau478/zig
5 participants
@andrewrk @squeek502 @Khitiara @Vexu @Arnau478