simplify now static function

git-svn-id: https://svn.r-project.org/R/trunk@87804 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: ripley

src/nmath/qbeta.c

@@ -48,14 +48,10 @@
 #define n_NEWTON_FREE 4
 //                   --- based on some testing; had = 10
 
-#define MLOGICAL_NA -1
-// an "NA_LOGICAL" substitute for Mathlib {only used here, for now}
-
-//attribute_hidden
 static void
 qbeta_raw(double alpha, double p, double q,
 	  Rboolean lower_tail, Rboolean log_p,
-	  int swap_01, double log_q_cut, int n_N, double* qb);
+	  double log_q_cut, int n_N, double* qb);
 
 /* This is the public interface in Rmath.h, so has to use 'int' */
 double qbeta(double alpha, double p, double q, int lower_tail, int log_p)
@@ -71,8 +67,8 @@ double qbeta(double alpha, double p, double q, int lower_tail, int log_p)
 
     double qbet[2];// = { qbeta(), 1 - qbeta() }
     qbeta_raw(alpha, p, q, lower_tail, log_p,
-	      // swap_01 ,  log_q_cut ,      n_N
-	      MLOGICAL_NA, USE_LOG_X_CUTOFF, n_NEWTON_FREE, qbet);
+	      // log_q_cut ,      n_N
+	      USE_LOG_X_CUTOFF, n_NEWTON_FREE, qbet);
     return qbet[0];
 }
 
@@ -111,21 +107,17 @@ static const double
 #define const4 0.04481
 
 // Returns both qbeta() and its "mirror" 1-qbeta(). Useful notably when qbeta() ~= 1
-// This was hidden, but it is only used in this file so could be static
-// and be simplifed as swap_01 is always NA.
 // attribute_hidden void
 static void
 qbeta_raw(double alpha, double p, double q,
 	  Rboolean lower_tail, Rboolean log_p,
-	  int swap_01, // {TRUE, NA, FALSE}: if NA, algorithm decides swap_tail
 	  double log_q_cut, /* if == Inf: return log(qbeta(..));
 			       otherwise, if finite: the bound for
 			       switching to log(x)-scale; see use_log_x */
 	  int n_N,  // number of "unconstrained" Newton steps before switching to constrained
 	  double *qb) // = qb[0:1] = { qbeta(), 1 - qbeta() }
 {
     Rboolean
-	swap_choose = (swap_01 == MLOGICAL_NA),
 	swap_tail,
 	log_, give_log_q = (log_q_cut == ML_POSINF),
 	use_log_x = give_log_q, // or u < log_q_cut  below
@@ -195,21 +187,20 @@ qbeta_raw(double alpha, double p, double q,
     // Conceptually,  0 < p_ < 1  (but can be 0 or 1 because of cancellation!)
     logbeta = lbeta(p, q);
 
-    // this is only ever called with swap_choose = TRUE
-    swap_tail = (swap_choose) ? (p_ > 0.5) : (Rboolean) swap_01;
+    swap_tail = (p_ > 0.5);
 
     R_ifDEBUG_printf(
-	"qbeta(%g, %g, %g, lower_t=%d, log_p=%d, swap_01=%d, log_q_cut=%g, n_N=%d):%s\n"
+	"qbeta(%g, %g, %g, lower_t=%d, log_p=%d, log_q_cut=%g, n_N=%d):%s\n"
 	"  swap_tail=%s :",
-	alpha, p,q, lower_tail, log_p, swap_01, log_q_cut, n_N,
+	alpha, p,q, lower_tail, log_p, log_q_cut, n_N,
 	(log_p && (p_ == 0. || p_ == 1.)) ? (p_==0.?" p_=0":" p_=1") : "",
 	(swap_tail ? "TRUE": "F"));
 
     int n_maybe_swaps = 0;
 maybe_swap:
-    // change tail; default (swap_01 = NA): afterwards 0 < a <= 1/2
+    // change tail; afterwards 0 < a <= 1/2
     if(swap_tail) { /* change tail, swap copies of {p,q}:  p <-> q :*/
-	a = R_DT_CIv(alpha); // = 1 - p_ , is < 1/2 if(swap_choose)
+	a = R_DT_CIv(alpha); // = 1 - p_ , is < 1/2
 	/* la := log(a), but without numerical cancellation: */
 	la = R_DT_Clog(alpha);
 	pp = q; qq = p;
@@ -346,7 +337,7 @@ qbeta_raw(double alpha, double p, double q,
     }
 
     // Problem: If initial u is completely wrong, we make a wrong decision here
-    if(swap_choose &&  //   vvvv/ why -exp(*)? u  on log-x scale! Swapping can be very good, but needs smart if(..)
+    if(
        (( swap_tail && u >= -exp(  log_q_cut)) || // ==> "swap back"
 	(!swap_tail && u >= -exp(4*log_q_cut) && pp / qq < 1000.) // ==> "swap now"
 	   )) {