From 9a1d25171690df1e83e3c8eb7187f6fc9a7d9698 Mon Sep 17 00:00:00 2001
From: Dimitri Lozeve <dimitri@lozeve.com>
Date: Mon, 11 Nov 2024 22:58:04 +0100
Subject: [PATCH] Fix issue with unsigned integers
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Fixes https://github.com/dlozeve/bqn-npy/issues/1.

The spec says that •bit._cast should support 32-bit uints [1], but
CBQN does not [2].

To get around this, we just use signed integers, which works for
numbers smaller than 2^31. Above that, it will wrap around
and (probably) fail, but CBQN does not support them anyway (except by
converting them to doubles).

From Marshall:

> All of the provided functions at this time are identical on i32 and
> u32, because they work (mod 2^32) and the only difference between
> those formats is to add or subtract 2^32 from numbers outside the
> range [0,2^31).
> If you want to run on u32s stored directly as numbers in BQN (they
> won't fit in i32 and will be stored as double!) you can •bit._cast
> those into a signed format at the beginning and then back out at the
> end.

[1] https://mlochbaum.github.io/BQN/spec/system.html#bitwise-operations
[2] https://matrix.to/#/!EjsgbQQNuTfHXQoiax:matrix.org/$PL2AYNlLQuYhPftdt7yw7rW9heiVEEeATte2zOt2BYk
---
 gentest.py | 12 +++++++++---
 npy.bqn    |  6 +++++-
 tests.bqn  |  4 ++--
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/gentest.py b/gentest.py
index 118fae8..1fa2b0f 100644
--- a/gentest.py
+++ b/gentest.py
@@ -1,12 +1,18 @@
+# /// script
+# dependencies = ["numpy"]
+# ///
+
 import numpy as np
 
+
 def main():
     for endianness in "<>":
         for typ in "fiu":
             for size in "48":
-                dtype=endianness + typ + size
-                arr = np.zeros((2,3,4), dtype=dtype)
+                dtype = endianness + typ + size
+                arr = np.zeros((2, 3, 4), dtype=dtype)
                 np.save(f"test{dtype}.npy", arr)
 
-if __name__ == '__main__':
+
+if __name__ == "__main__":
     main()
diff --git a/npy.bqn b/npy.bqn
index 7763026..d3e997d 100644
--- a/npy.bqn
+++ b/npy.bqn
@@ -4,7 +4,11 @@ lf←@+10
 magicString←(@+147)∾"NUMPY"
 
 # Type conversions
-dtypes‿formats←⟨"<f8","<i4","<u4"⟩‿⟨64‿'f',32‿'i',32‿'u'⟩
+
+# CBQN does not support other widths than 1 for 'u'. However, signed
+# and unsigned integers seem to have the same behavior for numbers
+# below 2⋆31.
+dtypes‿formats←⟨"<f8","<i4","<u4"⟩‿⟨64‿'f',32‿'i',1‿'u'⟩
 DtypeToFormat←{(⊑dtypes⊐<𝕩)⊑formats}
 ArrayToBytes←{⟨DtypeToFormat 𝕨,8‿'c'⟩•bit._cast 𝕩}
 ArrayFromBytes←{⟨8‿'c',DtypeToFormat 𝕨⟩•bit._cast 𝕩}
diff --git a/tests.bqn b/tests.bqn
index d5c953c..5ccb29c 100644
--- a/tests.bqn
+++ b/tests.bqn
@@ -1,8 +1,8 @@
 ⟨SaveNpy,LoadNpy⟩←•Import"npy.bqn"
 
 floatArr←2‿3•rand.Range 0
-intArr←50-˜2‿3•rand.Range 100
-uintArr←2‿3•rand.Range 100
+intArr←(2⋆31)-˜2‿3•rand.Range 2⋆32
+uintArr←2‿3•rand.Range 2⋆31
 
 "test_float.npy"SaveNpy floatArr
 "test_int.npy"SaveNpy intArr