commit 9b2e9b184ff5adb619c43b36086de0dd8ce9610b
Author: Dimitri Lozeve <dimitri@lozeve.com>
Date:   Wed Oct 4 13:26:25 2023 +0200

    Initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..56fa964
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*.npy
diff --git a/npy.bqn b/npy.bqn
new file mode 100644
index 0000000..7febe2a
--- /dev/null
+++ b/npy.bqn
@@ -0,0 +1,40 @@
+⟨SaveNpy,LoadNpy⟩⇐
+
+lf←@+10
+magicString←(@+147)∾"NUMPY"  # "\x93NUMPY"
+
+To_i16le←{@+256(|∾⌊∘÷˜)𝕩}
+# To_i16le←⟨16,8‿'c'⟩•bit._cast∘≍  # assumes the platform is little-endian
+FloatToBytes←⟨64,8‿'c'⟩•bit._cast
+
+FormatShape←{'('∾(1↓∾⥊','∾˘•Fmt¨≢𝕩)∾')'}
+
+BuildHeader←{𝕊𝕩:
+  version←1‿0
+  # Hypothesis: BQN arrays are C-contiguous
+  headerData←"{'descr': '<f8', 'fortran_order': False, 'shape': "∾(FormatShape 𝕩)∾", }"
+  padding←' '↑˜64-64|(≠magicString)+2+2+(≠headerData)+1
+  ! 0=64|(≠magicString)+2+2+(≠padding)+(≠headerData)+1
+  headerDataPadded←headerData∾padding∾lf
+  magicString∾(@+version)∾(To_i16le ≠headerDataPadded)∾headerDataPadded
+}
+
+EncodeNpy←BuildHeader∾FloatToBytes∘⥊
+
+SaveNpy←•file.Bytes⟜EncodeNpy
+
+ParseHeader←{𝕊𝕩:
+  "Not a valid NPY file"! magicString≡(≠magicString)↑𝕩
+  version←@-˜(0‿1+≠magicString)⊏𝕩
+  headerlen←+´1‿256×@-˜(2‿3+≠magicString)⊏𝕩
+  header←(¬∊⟜(' '∾lf))⊸/headerlen↑(4+≠magicString)↓𝕩
+  shapestr←(⊐⟜')'↑⊢) (1⊸+∘⊐⟜'('↓⊢) (("shape"⍷header)⊐1)↓header
+  shape←•BQN¨','((⊢-˜+`׬)∘=⊔⊢)shapestr
+  ⟨version,shape,headerlen+2+2+≠magicString⟩
+}
+
+LoadNpy←{𝕊𝕩:
+  bytes←•file.Bytes 𝕩
+  version‿shape‿datastart←ParseHeader bytes
+  shape⥊⟨8‿'c',64‿'f'⟩•bit._cast datastart↓bytes
+}
diff --git a/tests.bqn b/tests.bqn
new file mode 100644
index 0000000..ae49f0f
--- /dev/null
+++ b/tests.bqn
@@ -0,0 +1,7 @@
+⟨SaveNpy,LoadNpy⟩←•Import"npy.bqn"
+
+a←3‿4‿5•rand.Range 0
+"testbqn.npy"SaveNpy a
+b←LoadNpy"testbqn.npy"
+! a≡○≢b
+! a≡b