From 6352009def94b37534a6213760b0b6c65f2cda40 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Wed, 25 Dec 2019 08:04:09 -0600
Subject: [PATCH] sometimes-faster fixnum `/` via` quotient`

Try `fxquotient` with a `fx*` check to implement `/` on fixnums.
That's fast enough to be much faster when it works, and only slows
down a more general `/` a little.

original commit: e91430be9b71f4913965db688a15f6d7206b38f3
---
 s/5_3.ss | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/s/5_3.ss b/s/5_3.ss
index 0473addb0d..ae5746f768 100644
--- a/s/5_3.ss
+++ b/s/5_3.ss
@@ -2211,9 +2211,20 @@
 (set! $/
    (lambda (who x y)
       (type-case y
-         [(fixnum? bignum?)
+         [(fixnum?)
           (type-case x
-             [(fixnum? bignum?)
+             [(fixnum?)
+              ;; Trying `fxquotient` followed by a `fx*` check
+              ;; is so much faster (in the case that it works)
+              ;; that it's worth a try
+              (when (eq? y 0) (domain-error who y))
+              (if (fx= x (constant most-negative-fixnum))
+                  (integer/ x y) ; in case `y` is -1
+                  (let ([q (fxquotient x y)])
+                    (if (fx= x (fx* y q))
+                        q
+                        (integer/ x y))))]
+             [(bignum?)
               (when (eq? y 0) (domain-error who y))
               (integer/ x y)]
              [(ratnum?)
@@ -2226,6 +2237,18 @@
               (make-rectangular (/ (real-part x) y) (/ (imag-part x) y))]
              [(flonum?) (inexact-exact/ x y)]
              [else (nonnumber-error who x)])]
+         [(bignum?)
+          (type-case x
+             [(fixnum? bignum?)
+              (integer/ x y)]
+             [(ratnum?)
+              (/ ($ratio-numerator x) (* y ($ratio-denominator x)))]
+             [($exactnum?)
+              (make-rectangular (/ (real-part x) y) (/ (imag-part x) y))]
+             [($inexactnum?)
+              (make-rectangular (/ (real-part x) y) (/ (imag-part x) y))]
+             [(flonum?) (inexact-exact/ x y)]
+             [else (nonnumber-error who x)])]
          [(ratnum?)
           (type-case x
              [(fixnum? bignum?)