string.sha1 prints hex digits in a non-standard way

[Laupetin]

What seems to be the problem?
The hex string produced by the string.sha1 function prints the result in a non-standard way.
To be exact, for each byte it swaps the higher and lower 4 bits compared to what other implementations do.

So for example if one byte of the hash was 0xAF, the string would contain FA instead.

What did you expect to happen?

I expected the resulting string to match the output of other tools, e.g. sha1sum.

How can we reproduce this?

premake5.lua

require("premake", ">=5.0.0-beta7")
print(string.sha1(io.readfile("./test.txt")))

test.txt

foobar

What have you tried so far?

The problem seems to be here i guess:

premake-core/src/host/string_sha1.c

Lines 175 to 176 in ef05390

	output[i * 2 + 0] = g_int2hex[result[i] & 0x0f];
	output[i * 2 + 1] = g_int2hex[result[i] >> 4];

The code first adds the lower 4 bits to the string, then the upper 4 bits.
Standard way to print a hex string would however first print the upper 4 bits, then the lower 4 bits.

I would have made a PR, however this has been implemented this way for 10 years now, so I wasn't sure if this is even something that should be fixed or if it was left like this intentionally?
If it is something to fix, I can make one though.

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What version of Premake are you using?
premake5 (Premake Build Script Generator) 5.0.0-beta7

Anything else we should know?

[Jarod42]

Fixing it might break people using our method and comparing with previous computed one :-/