I am using generics here to work for other types as well, it 's not only for
converting int32[] slice to int64[], it is generic function to work for any
conversion like BytestoInt64/32/16/8, BytestoFloat32/64 etc.
It is failing for other conversion like BytestoInt64 , BytestoFloat64 etc on
big-endian machine but working on little endian .
________________________________
From: 'Pokala Srinivas' via golang-nuts <golang-nuts@googlegroups.com>
Sent: 08 May 2024 15:39
To: golang-nuts <golang-nuts@googlegroups.com>; Brian Candler
<bcandler...@googlemail.com>
Subject: [EXTERNAL] Re: [go-nuts] Re: Slice conversion function not working on
big endian platform
There is typo mistake while entering, below is the code snippest: package main
import ( "fmt" "unsafe" ) type slice struct { ptr unsafe. Pointer len int cap
int } func Slice[To, From any](data []From) []To { var zf From var
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There is typo mistake while entering, below is the code snippest:
package main
import (
"fmt"
"unsafe"
)
type slice struct {
ptr unsafe.Pointer
len int
cap int
}
func Slice[To, From any](data []From) []To {
var zf From
var zt To
var s = (*slice)(unsafe.Pointer(&data))
s.len = int((uintptr(s.len) * unsafe.Sizeof(zf)) / unsafe.Sizeof(zt))
s.cap = int((uintptr(s.cap) * unsafe.Sizeof(zf)) / unsafe.Sizeof(zt))
x := *(*[]To)(unsafe.Pointer(s))
return x
}
func main() {
a := make([]uint32, 4, 13)
a[0] = 1
a[1] = 0
a[2] = 2
a[3] = 0
// 1 0 2 0
b := Slice[int64](a)
//Expecxted : []int64[]{0x00000000 00000001, 0x00000000 00000002}
//Got: []int64{0x00000001 00000000, 0x00000002 0000000}
if b[0] != 1 {
fmt.Printf("wrong value at index 0: want=1 got=0x%x \n", b[0])
}
if b[1] != 2 {
fmt.Printf("wrong value at index 1: want=2 got=0x%x\n", b[0])
}
}
Please try this code
________________________________
From: 'Brian Candler' via golang-nuts <golang-nuts@googlegroups.com>
Sent: 08 May 2024 15:25
To: golang-nuts <golang-nuts@googlegroups.com>
Subject: [EXTERNAL] [go-nuts] Re: Slice conversion function not working on big
endian platform
That code doesn't even compile in go 1. 22 or go. 1. 21: https: //go.
dev/play/p/mPCBUQizSVo ./prog. go: 20: 14: cannot convert unsafe. Pointer(s)
(value of type unsafe. Pointer) to type []To What's the underlying requirement?
In the test case it looks
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That code doesn't even compile in go 1.22 or go.1.21:
https://go.dev/play/p/mPCBUQizSVo<https://go.dev/play/p/mPCBUQizSVo>
./prog.go:20:14: cannot convert unsafe.Pointer(s) (value of type
unsafe.Pointer) to type []To
What's the underlying requirement? In the test case it looks like you want to
take a slice of int32's, in whatever their internal in-memory representation
is, and re-represent them as a slice of half as many int64's?? Then of *course*
each pair of int32's will become one int64, and the order of the hi/lo halves
will depend entirely on the system's internal representation of int64's. It
*is* working, in the sense that it's doing exactly what you told it to do.
There's a reason why the "unsafe" package is called "unsafe"!
It would be straightforward to write a function which takes a slice containing
pairs of int32's and assembles them into int64's in a consistent way. What
you've not explained is:
- why you need to do this with generics (for example, what behaviour would you
expect from other types?)
- why you need to do this in-place with "unsafe"
On Wednesday 8 May 2024 at 10:24:30 UTC+1 Srinivas Pokala wrote:
Hello gopher's,
I have simple go program which convert slice of one type to slice of other type
using go generics for handling all the supported types.
Below is the code snippest for this:
package main
import "fmt"
import "unsafe"
type slice struct {
ptr unsafe.Pointer
len int
cap int
}
func Slice[To, From any](data []From) []To {
var zf From
var zt To
var s = (*slice)(unsafe.Pointer(&data))
s.len = int((uintptr(s.len) * unsafe.Sizeof(zf)) / unsafe.Sizeof(zt))
s.cap = int((uintptr(s.cap) * unsafe.Sizeof(zf)) / unsafe.Sizeof(zt))
x := ([]To)(unsafe.Pointer(s))
return x
}
func main() {
a := make([]uint32, 4, 13)
a[0] = 1
a[1] = 0
a[2] = 2
a[3] = 0
// 1 0 2 0
b := Slice[int64](a)
//Expecxted : []int64[]{0x00000000 00000001, 0x00000000 00000002}
//Got: []int64{0x00000001 00000000, 0x00000002 0000000}
if b[0] != 1 {
fmt.Printf("wrong value at index 0: want=1 got=0x%x \n", b[0])
}
if b[1] != 2 {
fmt.Printf("wrong value at index 1: want=2 got=0x%x\n", b[0])
}
}
This is working fine on little endian architectures(amd64,arm64 etc), but when
i run on big endian machine(s390x) it is not working , it is resulting wrong
data
//Expecxted : []int64[]{0x00000000 00000001, 0x00000000 00000002}
//Got: []int64{0x00000001 00000000, 0x00000002 0000000}
Can somepoint point me how do we write such scenario which should work on both
little/endian platforms.
Any leads on this?
Thanks,
Srinivas
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