Faster near-zero test?

Author: pavpanchekha

mpfr.rkt

@@ -162,6 +162,7 @@
          bfodd?
          bfcopy
          bfstep
+         bigfloat->flonum
          bigfloats-between
          bfprev
          bfnext

utils.rkt

@@ -1,8 +1,8 @@
 #lang racket/base
 
-(require "eval/machine.rkt")
-(require math/bigfloat
-         math/flonum)
+(require "mpfr.rkt"
+         "eval/machine.rkt")
+(require math/flonum)
 (provide flonum-discretization
          boolean-discretization
          bf-discretization)
@@ -11,12 +11,14 @@
 
 (define boolean-discretization (discretization 53 values (lambda (x y) (if (eq? x y) 0 2))))
 
+(define min-exponent (mpfr-exp (bfnext 0.bf)))
+
 (define (bf-discretization [precision #f])
   (define n (or precision (bf-precision)))
   (discretization n
                   (lambda (x)
                     (parameterize ([bf-precision n])
-                      (if (equal? (bigfloats-between 0.bf x) 1)
+                      (if (and (= (mpfr-exp x) min-exponent) (equal? (bigfloats-between 0.bf x) 1))
                           (bf 0)
                           (bfcopy x))))
                   (lambda (x y)