transmute slice from #load adjusts slice size

[ryhor-spivak]

package main
import "core:fmt"
main :: proc()
{
	embed_u32 := transmute([]u32) #load("embed") // 8 bytes file just like literal below
	src_u32 := transmute([]u32) []u8{31,32,33,34,35,36,37,38}
	fmt.printf( "embed_u32 len %d\nsrc_u32 len %d\n", len(embed_u32) , len(src_u32) )
}

This prints:
embed_u32 len 2
src_u32 len 8

Somehow transmuting []u8 slice returned by #load() readjusts slice length from 8 to 2. But with slice literal this doesn't work. As I understand mem.slice_data_cast should be used here. But it is very confusing why transmute([]u32) works differently on slices returned by #load()

    Odin: dev-2022-11-nightly:382bd876
    OS:   Windows 10 Unknown Edition (00000064) (version: 21H2), build 19044.2251
    CPU:  AMD Ryzen 7 5800HS with Radeon Graphics
    RAM:  15775 MiB

[gingerBill]

You are incorrectly using both #load and transmute.

transmute just reinterprets the bits to whatever type you specified.

What I am guessing you want wanting to use it the following:

#load("embed", []u32)

This will interpret the file as if it is an array of u32.

[Kelimion]

It is a bug, though. Make a file called eight.txt with contents 12345678, run this:

main :: proc() {
	DATA  :: #load("eight.txt")
	D32   :: transmute([]u32)#load("eight.txt")
	fmt.println(len(DATA), len(D32))
}

Prints: 8 2

This means that D32 :: transmute([]u32)#load("eight.txt") is treated as #load("eight.txt", []u32), even though if it had really been a transmute bit cast, the length would've remained 8.

Also interesting is that _D32 :: transmute([]u32)DATA gives you the expected error that you can't transmute a constant, but when used directly on #load as above it is allowed (and does the wrong thing).

Here you have the expected behavior that _D32 contains 8 elements despite having a backing for only 2, i.e. a user error. So the bug is either that transmute([]u32)#load is allowed, or that it doesn't evince the same user error.

main :: proc() {
	DATA  :: #load("eight.txt")
	D32   :: transmute([]u32)#load("eight.txt")
	fmt.println(len(DATA), len(D32))

	data  := DATA
	_D32  := transmute([]u32)data
	fmt.println(D32)
	fmt.println(_D32)
}