diff --git a/scheme/ikarus.not-yet-implemented.ss b/scheme/ikarus.not-yet-implemented.ss
index 9036c75..2bbc0a8 100644
--- a/scheme/ikarus.not-yet-implemented.ss
+++ b/scheme/ikarus.not-yet-implemented.ss
@@ -1,8 +1,8 @@
 
 (library (ikarus not-yet-implemented)
   (export 
-    bitwise-copy-bit-field bitwise-reverse-bit-field
-    bitwise-rotate-bit-field bitwise-if fxreverse-bit-field
+    bitwise-reverse-bit-field
+    bitwise-rotate-bit-field fxreverse-bit-field
     make-custom-binary-input/output-port
     make-custom-textual-input/output-port
     open-file-input/output-port output-port-buffer-mode
@@ -15,8 +15,8 @@
     string-upcase)
 
   (import (except (ikarus) 
-    bitwise-copy-bit-field bitwise-reverse-bit-field
-    bitwise-rotate-bit-field bitwise-if fxreverse-bit-field
+    bitwise-reverse-bit-field
+    bitwise-rotate-bit-field fxreverse-bit-field
     make-custom-binary-input/output-port
     make-custom-textual-input/output-port
     open-file-input/output-port output-port-buffer-mode
@@ -53,8 +53,7 @@
   (not-yet 
     ;;; should be implemented
     string-downcase string-titlecase string-upcase
-    bitwise-if
-    bitwise-rotate-bit-field bitwise-copy-bit-field bitwise-reverse-bit-field
+    bitwise-rotate-bit-field bitwise-reverse-bit-field
     fxreverse-bit-field 
     ;;; not top priority at the moment
     make-eqv-hashtable make-hashtable equal-hash
diff --git a/scheme/ikarus.numerics.ss b/scheme/ikarus.numerics.ss
index 5b30091..66086dd 100644
--- a/scheme/ikarus.numerics.ss
+++ b/scheme/ikarus.numerics.ss
@@ -370,10 +370,10 @@
 (library (ikarus generic-arithmetic)
   (export + - * / zero? = < <= > >= add1 sub1 quotient remainder
           modulo even? odd? bitwise-and bitwise-not bitwise-ior
-          bitwise-xor
+          bitwise-xor bitwise-if
           bitwise-arithmetic-shift-right bitwise-arithmetic-shift-left 
           bitwise-arithmetic-shift 
-          bitwise-length
+          bitwise-length bitwise-copy-bit-field 
           bitwise-copy-bit bitwise-bit-field
           positive? negative? expt gcd lcm numerator denominator
           exact-integer-sqrt
@@ -398,10 +398,10 @@
             remainder modulo even? odd? quotient+remainder number->string 
             bitwise-arithmetic-shift-right bitwise-arithmetic-shift-left
             bitwise-arithmetic-shift 
-            bitwise-length
+            bitwise-length bitwise-copy-bit-field 
             bitwise-copy-bit bitwise-bit-field
             positive? negative? bitwise-and bitwise-not bitwise-ior
-            bitwise-xor
+            bitwise-xor bitwise-if
             expt gcd lcm numerator denominator
             exact->inexact inexact floor ceiling round log
             exact-integer-sqrt min max abs real->flonum
@@ -1002,6 +1002,29 @@
       [(bignum? x) (foreign-call "ikrt_bnlognot" x)]
       [else (die 'bitwise-not "invalid argument" x)]))
 
+  (define (bitwise-if x y z)
+    (define who 'bitwise-if)
+    (define (err x) (die who "not an exact integer" x))
+    (unless (or (fixnum? x) (bignum? x)) (err x))
+    (unless (or (fixnum? y) (bignum? y)) (err y))
+    (unless (or (fixnum? z) (bignum? z)) (err z))
+    (bitwise-ior 
+      (bitwise-and x y)
+      (bitwise-and (bitwise-not x) z)))
+
+  (define (bitwise-copy-bit-field x i j n)
+    (define who 'bitwise-copy-bit-field)
+    (define (err x) (die who "not an exact integer" x))
+    (define (err2 x) (die who "index must be nonnegative" x))
+    (define (err3 x y) (die who "indices must be in nondescending order" x y))
+    (unless (or (fixnum? x) (bignum? x)) (err x))
+    (unless (or (fixnum? i) (bignum? i)) (err i))
+    (unless (or (fixnum? j) (bignum? j)) (err j))
+    (unless (or (fixnum? n) (bignum? n)) (err n))
+    (when (< i 0) (err2 i))
+    (when (< j i) (err3 i j))
+    (bitwise-if (sll (sub1 (sll 1 (- j i))) i) (sll n i) x))
+
   (define -
     (case-lambda
       [(x y) (binary- x y)]
diff --git a/scheme/last-revision b/scheme/last-revision
index 0a02468..3603fbf 100644
--- a/scheme/last-revision
+++ b/scheme/last-revision
@@ -1 +1 @@
-1572
+1573