R/guidetable.R

In Tinflex: A Universal Non-Uniform Random Number Generator

#############################################################################
##
##  Create guide table.
##  (R version)
##
#############################################################################

make.guidetable.R <- function(params) {
    
    ## Get number of interval.
    n.ivs <- ncol(params)-1
    
    ## Allocate memory for guide table.
    gt <- integer(n.ivs)
    
    ## Compute cumulative sums.
    Acum <- cumsum(params["A.ht", 1:n.ivs])
    A.ht.tot <- Acum[n.ivs]
    
    ## Compute average area for each interval.
    Astep <- A.ht.tot / n.ivs
    
    ## Create hash table (guide table).
    sum <- 0
    i <- 1
    for (j in 1:n.ivs) {
        while (isTRUE(Acum[i] < sum)) {
            i <- i+1
        }
        if (isTRUE(i > n.ivs)) {
            break;
        }
        gt[j] <- as.integer(i-1)   ## This is required for the C version.
        sum <- sum + Astep
    }
    
    ## If there has been an round off error,
    ## we have to complete the guide table.
    if (j<n.ivs) {
        for(jj in j:n.ivs) {
            gt[jj] <- n.ivs
        }
    }
    
    ## Return cumulative areas and hash table.
    return(list(Acum=Acum, gt=gt))

}  ## -- end of make.guidetable.R() -- ##

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## Remark:
## In C arrays are indexed using 0, 1, ..., length(array)-1
## In R arrays are indexed using 1, 2, ..., length(array)
## The guide table is primarily used by the C version.

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