Revert "Merge pull request #4938 from ollama/mxyng/fix-byte-order"

This reverts commit f5f245cc154580fa7b4052c001d2a7e3d771cfb8, reversing
changes made to 94d37fdcae30ddeb6c9f65c8707004f5ec9eaf33.

this change broke gguf v2 which is incorrectly detected as big endian

llm/ggml.go

@@ -231,7 +231,8 @@ const (
 	// Magic constant for `ggla` files (LoRA adapter).
 	FILE_MAGIC_GGLA = 0x67676C61
 	// Magic constant for `gguf` files (versioned, gguf)
-	FILE_MAGIC_GGUF = 0x46554747
+	FILE_MAGIC_GGUF_LE = 0x46554747
+	FILE_MAGIC_GGUF_BE = 0x47475546
 )
 
 var ErrUnsupportedFormat = errors.New("unsupported model format")
@@ -246,7 +247,7 @@ func DetectGGMLType(b []byte) string {
 		return "ggjt"
 	case FILE_MAGIC_GGLA:
 		return "ggla"
-	case FILE_MAGIC_GGUF:
+	case FILE_MAGIC_GGUF_LE, FILE_MAGIC_GGUF_BE:
 		return "gguf"
 	default:
 		return ""
@@ -254,19 +255,21 @@ func DetectGGMLType(b []byte) string {
 }
 
 func DecodeGGML(rs io.ReadSeeker) (*GGML, int64, error) {
-	var magic [4]byte
+	var magic uint32
 	if err := binary.Read(rs, binary.LittleEndian, &magic); err != nil {
 		return nil, 0, err
 	}
 
 	var c container
-	switch binary.LittleEndian.Uint32(magic[:]) {
+	switch magic {
 	case FILE_MAGIC_GGML, FILE_MAGIC_GGMF, FILE_MAGIC_GGJT:
 		return nil, 0, ErrUnsupportedFormat
 	case FILE_MAGIC_GGLA:
 		c = &containerGGLA{}
-	case FILE_MAGIC_GGUF:
+	case FILE_MAGIC_GGUF_LE:
 		c = &containerGGUF{ByteOrder: binary.LittleEndian}
+	case FILE_MAGIC_GGUF_BE:
+		c = &containerGGUF{ByteOrder: binary.BigEndian}
 	default:
 		return nil, 0, errors.New("invalid file magic")
 	}

llm/gguf.go

@@ -36,23 +36,10 @@ func (c *containerGGUF) Name() string {
 }
 
 func (c *containerGGUF) Decode(rs io.ReadSeeker) (model, error) {
-	var version [4]byte
-	if err := binary.Read(rs, c.ByteOrder, &version); err != nil {
+	if err := binary.Read(rs, c.ByteOrder, &c.Version); err != nil {
 		return nil, err
 	}
 
-	// if the lower 16 bits are 0, the byte order is probably wrong
-	if c.ByteOrder.Uint32(version[:])&1<<4 == 0 {
-		switch c.ByteOrder {
-		case binary.LittleEndian:
-			c.ByteOrder = binary.BigEndian
-		case binary.BigEndian:
-			c.ByteOrder = binary.LittleEndian
-		}
-	}
-
-	c.Version = c.ByteOrder.Uint32(version[:])
-
 	var err error
 	switch c.Version {
 	case 1: