From 1ac63d456439978ed0badbf7e94fe085402466c6 Mon Sep 17 00:00:00 2001
From: Gertjan van den Burg <gertjanvandenburg@gmail.com>
Date: Fri, 31 Jul 2015 00:04:46 +0200
Subject: added randbelow and shuffle methods

---
 SyncRNG.R | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

(limited to 'SyncRNG.R')

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)
 		}
 		)
 	)
-- 
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