Initial support for gambit-scheme v4.7.0

ports/gambc_ppapi/scm/pi.scm

+(define (pi num)
+  (define (pi-brent-salamin-approximate base k) ; k is number of digits
+    (define base^k (expt base k))
+    (define (fixed.+ x y)
+      (+ x y))
+
+    (define (fixed.- x y)
+      (- x y))
+
+    (define (fixed.* x y)
+      (quotient (* x y) base^k))
+
+    (define (fixed.square x)
+      (fixed.* x x))
+
+    (define (fixed./ x y)
+      (quotient (* x base^k) y))
+
+    (define (fixed.sqrt x)
+      (integer-sqrt (* x base^k)))
+
+    (define (number->fixed x)
+      (round (* x base^k)))
+
+    (define (fixed->number x)
+      (/ x base^k))
+
+    (let ((one (number->fixed 1)))
+      (let loop ((a one)
+                 (b (fixed.sqrt (quotient one 2)))
+                 (t (quotient one 4))
+                 (x 1))
+        (if (= a b)
+          (quotient (* a a) t)
+          (let ((new-a (quotient (fixed.+ a b) 2)))
+            (loop new-a
+                  (integer-sqrt (* a b))
+                  (fixed.- t (* x (fixed.square (fixed.- new-a a))))
+                  (* 2 x)))))))
+
+  (define (pi-brent-salamin base k) ; k is number of digits
+    (let ((n (ceiling (inexact->exact (+ 2 (log k))))))
+      (quotient (pi-brent-salamin-approximate base (+ k n)) (expt base n))))
+
+  (pi-brent-salamin-approximate 10 num))