added randbelow and shuffle methods

2 files changed, 55 insertions, 1 deletions

diff --git a/SyncRNG.R b/SyncRNG.R
index 1849d89..ca25eef 100644
--- a/SyncRNG.R
+++ b/SyncRNG.R
@@ -5,10 +5,12 @@ dyn.load('RSyncRNG.so')
 SyncRNG <- setRefClass('SyncRNG',
 	fields=list(
 		    seed='numeric',
-		    state='numeric'
+		    state='numeric',
+		    BPF='numeric'
 		    ),
 	methods=list(
 		initialize=function(..., seed=0) {
+			BPF <<- 32
 			seed <<- seed
 			tmp <- .Call('R_syncrng_seed',
 			     as.numeric(seed))
@@ -24,6 +26,32 @@ SyncRNG <- setRefClass('SyncRNG',
 		rand=function() {
 			r <- randi()
 			return (r * 2.3283064365387e-10)
+		},
+		randbelow=function(n) {
+			maxsize <- 2^BPF
+			if (n >= maxsize) {
+				warning(paste("Underlying random generator ",
+					     "does not supply\n enough bits ",
+					     "to choose from a population ",
+					     "range this large.\n"))
+				return(round(rand() * n))
+			}
+			rem <- maxsize %% n
+			limit <- (maxsize - rem) / maxsize
+			r <- rand()
+			while (r >= limit)
+				r <- rand()
+			return(round(r*maxsize) %% n)
+		},
+		shuffle=function(x) {
+			y <- x
+			for (i in rev(1:(length(y)-1))) {
+				j <- randbelow(i+1)
+				tmp <- y[i+1]
+				y[i+1] <- y[j+1]
+				y[j+1] <- tmp
+			}
+			return(y)
 		}
 		)
 	)
diff --git a/SyncRNG.py b/SyncRNG.py
index 7137439..7ef6fd6 100644
--- a/SyncRNG.py
+++ b/SyncRNG.py
@@ -4,11 +4,16 @@ used to seed and pull numbers from the RNG.
 
 """
 
+from __future__ import division
+
+from warnings import warn as _warn
+
 import syncrng
 
 class SyncRNG(object):
 
     def __init__(self, seed=0):
+        self.BPF = 32
         self.seed = seed
         self.state = syncrng.seed(seed)
 
@@ -19,3 +24,24 @@ class SyncRNG(object):
 
     def rand(self):
         return self.randi() * 2.3283064365387e-10
+
+    def randbelow(self, n):
+        maxsize = 1<<self.BPF
+        if n >= maxsize:
+            _warn("Underlying random generator does not supply \n"
+                    "enough bits to choose from a population range this "
+                    "large.\n")
+            return int(self.rand() * n)
+        rem = maxsize % n
+        limit = (maxsize - rem) / maxsize
+        r = self.rand()
+        while r >= limit:
+            r = self.rand()
+        return int(r*maxsize) % n
+
+    def shuffle(self, x):
+        y = x[:]
+        for i in reversed(range(1, len(y))):
+            j = self.randbelow(i+1)
+            y[i], y[j] = y[j], y[i]
+        return y