Add Dtype.lean

Data types with byte order. A small file, so
we may want to merge this with other files in the
future.

TensorLib/Basic.lean

@@ -5,3 +5,4 @@ Authors: Jean-Baptiste Tristan, Paul Govereau, Sean McLaughlin
 -/
 
 import TensorLib.Common
+import TensorLib.Dtype

TensorLib/Dtype.lean

@@ -0,0 +1,66 @@
+/-
+Copyright (c) 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Jean-Baptiste Tristan, Paul Govereau, Sean McLaughlin
+-/
+
+import TensorLib.Common
+
+namespace TensorLib
+namespace Dtype
+
+/-! The subset of types NumPy supports that we care about -/
+inductive Name where
+| bool
+| int8
+| int16
+| int32
+| int64
+| uint8
+| uint16
+| uint32
+| uint64
+| float16
+| float32
+| float64
+deriving BEq, Repr, Inhabited
+
+namespace Name
+
+instance : ToString Name where
+  toString x := (repr x).pretty
+
+def isMultiByte (x : Name) : Bool := match x with
+| bool | int8 | uint8 => false
+| _ => true
+
+--! Number of bytes used by each element of the given dtype
+def itemsize (x : Name) : Nat := match x with
+| float64 | int64 | uint64 => 8
+| float32 | int32 | uint32 => 4
+| float16 | int16 | uint16 => 2
+| bool | int8 | uint8 => 1
+
+end Name
+end Dtype
+
+structure Dtype where
+  name : Dtype.Name
+  order : ByteOrder
+deriving BEq, Repr, Inhabited
+
+namespace Dtype
+
+def byteOrderOk (x : Dtype) : Prop := !x.name.isMultiByte || (x.name.isMultiByte && x.order.isMultiByte)
+
+def itemsize (t : Dtype) := t.name.itemsize
+
+def sizedStrides (dtype : Dtype) (s : Shape) : Strides := List.map (fun x => x * dtype.itemsize) s.cUnitStrides
+
+def int8 : Dtype := Dtype.mk Dtype.Name.int8 ByteOrder.littleEndian
+def uint8 : Dtype := Dtype.mk Dtype.Name.uint8 ByteOrder.littleEndian
+def uint64 : Dtype := Dtype.mk Dtype.Name.uint64 ByteOrder.littleEndian
+def float64 : Dtype := Dtype.mk Dtype.Name.float64 ByteOrder.littleEndian
+
+end Dtype
+end TensorLib