Minor MPFR fix to avoid potential hysteresis effects resulting in higher-than-needed precision.

2 files changed, 15 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 28836da2..f370fdc9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2016-08-01         Andrew J. Schorr     <aschorr@telemetry-investments.com>
 
+	* mpfr.c (mpg_tofloat): Always set precision to avoid hysteresis effects
+	from previous calculations using the same temporary mpfr variables.
+
+2016-08-01         Andrew J. Schorr     <aschorr@telemetry-investments.com>
+
 	* mpfr.c (default_prec): Add new static variable to show current PREC
 	setting in effect.
 	(init_mpfr, set_PREC): Save mpfr_set_default_prec argument in
diff --git a/mpfr.c b/mpfr.c
index 0f602898..db2eb697 100644
--- a/mpfr.c
+++ b/mpfr.c
@@ -1218,9 +1218,17 @@ mpg_tofloat(mpfr_ptr mf, mpz_ptr mz)
 		prec -= (size_t) mpz_scan1(mz, 0);	/* least significant 1 bit index starting at 0 */
 		if (prec > MPFR_PREC_MAX)
 			prec = MPFR_PREC_MAX;
-		if (prec > PRECISION_MIN) 
-			mpfr_set_prec(mf, prec);
+		else if (prec < PRECISION_MIN)
+			prec = PRECISION_MIN;
 	}
+	else
+		prec = PRECISION_MIN;
+	/*
+	 * Always set the precision to avoid hysteresis, since do_mpfr_func 
+	 * may copy our precision.
+	 */
+	if (prec != mpfr_get_prec(mf))
+		mpfr_set_prec(mf, prec);
 
 	mpfr_set_z(mf, mz, ROUND_MODE);
 	return mf;