Added inline hint around `index?' definition; my own timing suggests 2x speedup

collects/typed-racket/types/numeric-predicates.rkt

@@ -1,14 +1,19 @@
 #lang racket/base
 
-(require racket/unsafe/ops)
+(require racket/unsafe/ops
+         racket/performance-hint)
 
 (provide index? exact-rational?)
 
 ;; this is required for template in numeric-tower.rkt
 
+(begin-encourage-inline
+
 ;; we assume indexes are 2 bits shorter than fixnums
 ;; We're generating a reference to fixnum? rather than calling it, so
 ;; we're safe from fixnum size issues on different platforms.
 (define (index? x) (and (fixnum? x) (unsafe-fx>= x 0) (fixnum? (* x 4))))
 
 (define (exact-rational? x) (and (rational? x) (exact? x)))
+
+) ; begin-encourage-inline