From c19ccd0a068869fa2a579b94dcb59b556f38b692 Mon Sep 17 00:00:00 2001
From: Jan Midtgaard <mail@janmidtgaard.dk>
Date: Tue, 22 Mar 2022 15:32:06 +0100
Subject: [PATCH] improved int shrinker

---
 src/core/QCheck.ml | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/core/QCheck.ml b/src/core/QCheck.ml
index 0526c7a3..a375f62c 100644
--- a/src/core/QCheck.ml
+++ b/src/core/QCheck.ml
@@ -650,14 +650,17 @@ module Shrink = struct
 
   let unit = nil
 
-  (* balanced shrinker for integers (non-exhaustive) *)
+  (* inspired by QCheck2's int shrinker algorithm (non-exhaustive) *)
   let int x yield =
-    let y = ref x in
+    let curr = ref 0 in (*to return 0 repeatedly *)  (*was: let curr = ref (x/2) *)
     (* try some divisors *)
-    while !y < -2 || !y >2 do y := !y / 2; yield (x - !y); done; (* fast path *)
-    if x>0 then yield (x-1);
-    if x<0 then yield (x+1);
-    ()
+    while !curr <> x do
+      yield !curr;
+      let half_diff = (x - !curr)/2 in (*was: let half_diff = (x/2) - (!curr/2) in *)
+      if half_diff = 0
+      then curr := x
+      else curr := !curr + half_diff
+    done
 
   let int32 x yield =
     let open Int32 in