Account for divisor truncation error as well as mpn_mu_divappr_q's error.

2 files changed, 8 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index d97b16136..0d2d200e0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,9 @@
 
 	* Version 5.0.0 released.
 
+	* mpn/generic/mu_div_q.c: Account for divisor truncation error as well
+	as mpn_mu_divappr_q's error.
+
 	* mpn/generic/mu_div_q.c: Handle mpn_preinv_mu_divappr_q returning a
 	high limb.
 
@@ -18,8 +21,8 @@
 	(mpn_preinv_mu_divappr_q, mpn_mu_divappr_q): Declare dividend constant.
 	* gmp-impl.h: Likewise.
 
-	* perfpow.c (mpn_perfect_power_p): Call mpn_divexact instead of mpn_bdiv_q (with
-	too little scratch space!).
+	* perfpow.c (mpn_perfect_power_p): Call mpn_divexact instead of
+	mpn_bdiv_q (with too little scratch space!).
 
 	From Niels Möller:
 	* tests/mpn/t-div.c (check_one): Get rid of the poorly managed variable
diff --git a/mpn/generic/mu_div_q.c b/mpn/generic/mu_div_q.c
index f0466a212..d4c3cef54 100644
--- a/mpn/generic/mu_div_q.c
+++ b/mpn/generic/mu_div_q.c
@@ -166,7 +166,9 @@ mpn_mu_div_q (mp_ptr qp,
       qh = mpn_mu_divappr_q (tp, np + nn - (2 * qn + 2), 2 * qn + 2,
 			     dp + dn - (qn + 1), qn + 1, scratch);
 
-      if (tp[0] > 4)
+      /* The max error of mpn_mu_divappr_q is +4, but we get an additional
+         error from the divisor truncation.  */
+      if (tp[0] > 6)
 	{
 	  MPN_COPY (qp, tp + 1, qn);
 	}