Zubin pushed to branch wip/9.12.3-backports at Glasgow Haskell Compiler / GHC Commits: 01e82a3c by Reed Mullanix at 2025-08-21T15:17:59+05:30 ghc-internal: Fix naturalAndNot for NB/NS case When the first argument to `naturalAndNot` is larger than a `Word` and the second is `Word`-sized, `naturalAndNot` will truncate the result: ```

...

...

naturalAndNot ((2 ^ 65) .|. (2 ^ 3)) (2 ^ 3) 0

In contrast, `naturalAndNot` does not truncate when both arguments are larger than a `Word`, so this appears to be a bug.
Luckily, the fix is pretty easy: we just need to call `bigNatAndNotWord#` instead of truncating.

Fixes #26230

(cherry picked from commit a766286fe759251eceb304c54ba52841c2a51f86)

- - - - -


6 changed files:

- libraries/base/changelog.md
- libraries/ghc-bignum/changelog.md
- libraries/ghc-bignum/src/GHC/Num/Natural.hs
- + testsuite/tests/numeric/should_run/T26230.hs
- + testsuite/tests/numeric/should_run/T26230.stdout
- testsuite/tests/numeric/should_run/all.T


Changes:

=====================================
libraries/base/changelog.md
=====================================
@@ -1,5 +1,8 @@
 # Changelog for [`base` package](http://hackage.haskell.org/package/base)
 
+## 4.21.2.0 *Sept 2024*
+  * Fix bug where `naturalAndNot` was incorrectly truncating results ([CLC proposal #350](github.com/haskell/core-libraries-committee/issues/350))
+
 ## 4.21.1.0 *Sept 2024*
   * Fix incorrect results of `integerPowMod` when the base is 0 and the exponent is negative, and `integerRecipMod` when the modulus is zero ([#26017](https://gitlab.haskell.org/ghc/ghc/-/issues/26017)).
 


=====================================
libraries/ghc-bignum/changelog.md
=====================================
@@ -4,6 +4,7 @@
 
 - Expose backendName
 - Add `naturalSetBit[#]` (#21173), `naturalClearBit[#]` (#21175), `naturalComplementBit[#]` (#21181)
+- Fix bug where `naturalAndNot` was incorrectly truncating results (#26230)
 
 ## 1.2
 


=====================================
libraries/ghc-bignum/src/GHC/Num/Natural.hs
=====================================
@@ -488,7 +488,7 @@ naturalAndNot :: Natural -> Natural -> Natural
 {-# NOINLINE naturalAndNot #-}
 naturalAndNot (NS n) (NS m) = NS (n `and#` not# m)
 naturalAndNot (NS n) (NB m) = NS (n `and#` not# (bigNatToWord# m))
-naturalAndNot (NB n) (NS m) = NS (bigNatToWord# n `and#` not# m)
+naturalAndNot (NB n) (NS m) = NB (bigNatAndNotWord# n m)
 naturalAndNot (NB n) (NB m) = naturalFromBigNat# (bigNatAndNot n m)
 
 naturalOr :: Natural -> Natural -> Natural


=====================================
testsuite/tests/numeric/should_run/T26230.hs
=====================================
@@ -0,0 +1,8 @@
+import Data.Bits
+import GHC.Num.Natural
+
+main = do
+  print $ naturalAndNot ((2 ^ 4) .|. (2 ^ 3)) (2 ^ 3)
+  print $ naturalAndNot ((2 ^ 129) .|. (2 ^ 65)) (2 ^ 65)
+  print $ naturalAndNot ((2 ^ 4) .|. (2 ^ 3)) ((2 ^ 65) .|. (2 ^ 3))
+  print $ naturalAndNot ((2 ^ 65) .|. (2 ^ 3)) (2 ^ 3)


=====================================
testsuite/tests/numeric/should_run/T26230.stdout
=====================================
@@ -0,0 +1,4 @@
+16
+680564733841876926926749214863536422912
+16
+36893488147419103232


=====================================
testsuite/tests/numeric/should_run/all.T
=====================================
@@ -87,3 +87,4 @@ test('T24066', normal, compile_and_run, [''])
 test('div01', normal, compile_and_run, [''])
 test('T24245', normal, compile_and_run, [''])
 test('T25653', normal, compile_and_run, [''])
+test('T26230', normal, compile_and_run, [''])



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/01e82a3cd7cd63432b0f64fc10252d21564324ee

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/01e82a3cd7cd63432b0f64fc10252d21564324ee
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