Adapted from this blog
Last active
December 11, 2023 02:09
-
-
Save nicerobot/832cf3a388e54b44f1c5 to your computer and use it in GitHub Desktop.
Alias a []float64 slice as a []byte slice
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| package main | |
| import ( | |
| "encoding/binary" | |
| "unsafe" | |
| ) | |
| // Returns a slice of the bytes of the provided float64 slice. | |
| // This allows highly performant access to large float64 slices for such things | |
| // as computing hashes or simply writing the bytes to a file. | |
| // BEWARE: this also means this []byte _is platform dependent_. | |
| func float64SliceAsByteSlice(floats []float64) ([]byte, binary.ByteOrder) { | |
| lf := 8 * len(floats) | |
| // step by step | |
| pf := &(floats[0]) // To pointer to the first byte of b | |
| up := unsafe.Pointer(pf) // To *special* unsafe.Pointer, it can be converted to any pointer | |
| pi := (*[1]byte)(up) // To pointer as byte array | |
| buf := (*pi)[:] // Creates slice to our array of 1 byte | |
| address := unsafe.Pointer(&buf) // Capture the address to the slice structure | |
| lenAddr := uintptr(address) + uintptr(8) // Capture the address where the length and cap size is stored | |
| capAddr := uintptr(address) + uintptr(16) // WARNING: This is fragile, depending on a go-internal structure. | |
| lenPtr := (*int)(unsafe.Pointer(lenAddr)) // Create pointers to the length and cap size | |
| capPtr := (*int)(unsafe.Pointer(capAddr)) // | |
| *lenPtr = lf // Assign the actual slice size and cap | |
| *capPtr = lf // | |
| return buf, nativeEndianness | |
| } | |
| var nativeEndianness binary.ByteOrder | |
| func init() { | |
| var i int32 = 0x01020304 | |
| u := unsafe.Pointer(&i) | |
| pb := (*byte)(u) | |
| b := *pb | |
| if b == 0x04 { | |
| nativeEndianness = binary.LittleEndian | |
| } else { | |
| nativeEndianness = binary.BigEndian | |
| } | |
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| package main | |
| import ( | |
| "math" | |
| "testing" | |
| ) | |
| // | |
| func TestUnsafeFloatToByte(t *testing.T) { | |
| fa := make([]float64, 2) | |
| fa[0] = math.MaxFloat64 | |
| fa[1] = -math.MaxFloat64 | |
| t.Logf("floats before: %v", fa) | |
| ba, end := float64SliceAsByteSlice(fa) | |
| t.Logf("%v", end) | |
| t.Logf("floats as bytes before: %v", ba) | |
| // This swaps the values in fa[0] and fa[1] | |
| ba[7], ba[15] = ba[15], ba[7] | |
| t.Logf("floats as bytes after: %v", ba) | |
| t.Logf("floats after: %v", fa) | |
| if fa[0] != -math.MaxFloat64 { | |
| t.Error("fa[0] not negative") | |
| } | |
| if fa[1] != math.MaxFloat64 { | |
| t.Error("fa[1] not positive") | |
| } | |
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| .PHONY: test | |
| test: | |
| go test -v |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment