Add a function to write gguf files. (#585)

* Add a function to write gguf files.

* More GGUF file writing.

* Write the tensor data in GGUF files.

candle-core/src/quantized/gguf_file.rs

@@ -4,7 +4,7 @@
 
 use super::{GgmlDType, QTensor};
 use crate::Result;
-use byteorder::{LittleEndian, ReadBytesExt};
+use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 use std::collections::HashMap;
 
 pub const DEFAULT_ALIGNMENT: u64 = 32;
@@ -19,7 +19,7 @@ impl TryFrom<u32> for Magic {
     fn try_from(value: u32) -> Result<Self> {
         let magic = match value {
             0x46554747 | 0x47475546 => Self::Gguf,
-            _ => crate::bail!("unknown magic {value:08x}"),
+            _ => crate::bail!("unknown magic 0x{value:08x}"),
         };
         Ok(magic)
     }
@@ -86,7 +86,7 @@ fn read_string<R: std::io::Read>(reader: &mut R) -> Result<String> {
     Ok(String::from_utf8_lossy(&v).into_owned())
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum ValueType {
     // The value is a 8-bit unsigned integer.
     U8,
@@ -129,6 +129,21 @@ pub enum Value {
 }
 
 impl Value {
+    pub fn value_type(&self) -> ValueType {
+        match self {
+            Self::U8(_) => ValueType::U8,
+            Self::I8(_) => ValueType::I8,
+            Self::U16(_) => ValueType::U16,
+            Self::I16(_) => ValueType::I16,
+            Self::U32(_) => ValueType::U32,
+            Self::I32(_) => ValueType::I32,
+            Self::F32(_) => ValueType::F32,
+            Self::Bool(_) => ValueType::Bool,
+            Self::String(_) => ValueType::String,
+            Self::Array(_) => ValueType::Array,
+        }
+    }
+
     pub fn to_u8(&self) -> Result<u8> {
         match self {
             Self::U8(v) => Ok(*v),
@@ -227,6 +242,41 @@ impl Value {
         };
         Ok(v)
     }
+
+    fn write<W: std::io::Write>(&self, w: &mut W) -> Result<()> {
+        match self {
+            &Self::U8(v) => w.write_u8(v)?,
+            &Self::I8(v) => w.write_i8(v)?,
+            &Self::U16(v) => w.write_u16::<LittleEndian>(v)?,
+            &Self::I16(v) => w.write_i16::<LittleEndian>(v)?,
+            &Self::U32(v) => w.write_u32::<LittleEndian>(v)?,
+            &Self::I32(v) => w.write_i32::<LittleEndian>(v)?,
+            &Self::F32(v) => w.write_f32::<LittleEndian>(v)?,
+            &Self::Bool(v) => w.write_u8(u8::from(v))?,
+            Self::String(v) => write_string(w, v.as_str())?,
+            Self::Array(v) => {
+                // The `Value` type does not enforce that all the values in an Array have the same
+                // type.
+                let value_type = if v.is_empty() {
+                    // Doesn't matter, the array is empty.
+                    ValueType::U32
+                } else {
+                    let value_type: std::collections::HashSet<_> =
+                        v.iter().map(|elem| elem.value_type()).collect();
+                    if value_type.len() != 1 {
+                        crate::bail!("multiple value-types in the same array {value_type:?}")
+                    }
+                    value_type.into_iter().next().unwrap()
+                };
+                w.write_u32::<LittleEndian>(value_type.to_u32())?;
+                w.write_u32::<LittleEndian>(v.len() as u32)?;
+                for elem in v.iter() {
+                    elem.write(w)?
+                }
+            }
+        }
+        Ok(())
+    }
 }
 
 impl ValueType {
@@ -246,6 +296,21 @@ impl ValueType {
         };
         Ok(v)
     }
+
+    fn to_u32(self) -> u32 {
+        match self {
+            Self::U8 => 0,
+            Self::I8 => 1,
+            Self::U16 => 2,
+            Self::I16 => 3,
+            Self::U32 => 4,
+            Self::I32 => 5,
+            Self::F32 => 6,
+            Self::Bool => 7,
+            Self::String => 8,
+            Self::Array => 9,
+        }
+    }
 }
 
 impl Content {
@@ -312,3 +377,60 @@ impl Content {
         tensor_info.read(reader, self.tensor_data_offset)
     }
 }
+
+fn write_string<W: std::io::Write>(w: &mut W, str: &str) -> Result<()> {
+    let bytes = str.as_bytes();
+    w.write_u32::<LittleEndian>(bytes.len() as u32)?;
+    w.write_all(bytes)?;
+    Ok(())
+}
+
+pub fn write<W: std::io::Seek + std::io::Write>(
+    w: &mut W,
+    metadata: &[(&str, &Value)],
+    tensors: &[(&str, &QTensor)],
+) -> Result<()> {
+    w.write_u32::<LittleEndian>(0x46554747)?;
+    w.write_u32::<LittleEndian>(1)?; // version 1.
+    w.write_u32::<LittleEndian>(tensors.len() as u32)?;
+    for (name, value) in metadata.iter() {
+        write_string(w, name)?;
+        w.write_u32::<LittleEndian>(value.value_type().to_u32())?;
+        value.write(w)?;
+    }
+    let mut offset = 0usize;
+    let mut offsets = Vec::with_capacity(tensors.len());
+    for (name, tensor) in tensors.iter() {
+        write_string(w, name)?;
+        let dims = tensor.shape().dims();
+        w.write_u32::<LittleEndian>(dims.len() as u32)?;
+        for &dim in dims.iter().rev() {
+            w.write_u32::<LittleEndian>(dim as u32)?;
+        }
+        w.write_u32::<LittleEndian>(tensor.dtype().to_u32())?;
+        w.write_u64::<LittleEndian>(offset as u64)?;
+        offsets.push(offset);
+        let size_in_bytes = tensor.storage_size_in_bytes();
+        let padding = 31 - (31 + size_in_bytes) % 32;
+        offset += size_in_bytes + padding;
+    }
+    let pos = w.stream_position()? as usize;
+    let padding = 31 - (31 + pos) % 32;
+    w.write_all(&vec![0u8; padding])?;
+    let tensor_start_pos = w.stream_position()? as usize;
+    for (offset, (_name, tensor)) in offsets.iter().zip(tensors.iter()) {
+        let pos = w.stream_position()? as usize;
+        if tensor_start_pos + offset != pos {
+            crate::bail!(
+                "internal error, unexpected current position {tensor_start_pos} {offset} {pos}"
+            )
+        }
+        let data_ptr = tensor.as_ptr();
+        let size_in_bytes = tensor.storage_size_in_bytes();
+        let data = unsafe { std::slice::from_raw_parts(data_ptr, size_in_bytes) };
+        w.write_all(data)?;
+        let padding = 31 - (31 + size_in_bytes) % 32;
+        w.write_all(&vec![0u8; padding])?;
+    }
+    Ok(())
+}