diff --git a/doc/fmprb.txt b/doc/fmprb.txt
index 52244834..0275fd4e 100644
--- a/doc/fmprb.txt
+++ b/doc/fmprb.txt
@@ -451,6 +451,10 @@ void fmprb_const_pi(fmprb_t x, long prec)
 
     Sets x to $\pi$. The value is cached for repeated use.
 
+void fmprb_const_log_sqrt2pi(fmprb_t x, long prec)
+
+    Sets x to $\log \sqrt{2 \pi}$. The value is cached for repeated use.
+
 void fmprb_const_euler_brent_mcmillan(fmprb_t res, long prec)
 
     Sets x to Euler's constant $\gamma$, computed using the second
diff --git a/fmprb.h b/fmprb.h
index 8071add4..14c1b7f8 100644
--- a/fmprb.h
+++ b/fmprb.h
@@ -234,6 +234,8 @@ void fmprb_fib_ui(fmprb_t f, ulong n, long prec);
 void fmprb_const_pi_chudnovsky(fmprb_t x, long prec);
 void fmprb_const_pi(fmprb_t x, long prec);
 
+void fmprb_const_log_sqrt2pi(fmprb_t t, long prec);
+
 void fmprb_const_euler_brent_mcmillan(fmprb_t res, long prec);
 void fmprb_const_zeta3_bsplit(fmprb_t x, long prec);
 
@@ -329,5 +331,22 @@ void fmprb_randtest(fmprb_t x, flint_rand_t state, long prec, long mag_bits);
 
 void fmprb_get_rand_fmpq(fmpq_t q, flint_rand_t state, const fmprb_t x, long bits);
 
+/* TODO: this should be threadsafe */
+#define DEF_CACHED_CONSTANT(name, comp_func) \
+    long name ## _cached_prec = 0; \
+    fmprb_t name ## _cached_value; \
+    void \
+    name(fmprb_t x, long prec) \
+    { \
+        if (name ## _cached_prec < prec) \
+        { \
+            if (name ## _cached_prec == 0) \
+                fmprb_init(name ## _cached_value); \
+            comp_func(name ## _cached_value, prec); \
+            name ## _cached_prec = prec; \
+        } \
+        fmprb_set_round(x, name ## _cached_value, prec); \
+    } \
+
 #endif
 
diff --git a/fmprb/const_log_sqrt2pi.c b/fmprb/const_log_sqrt2pi.c
new file mode 100644
index 00000000..4c33daed
--- /dev/null
+++ b/fmprb/const_log_sqrt2pi.c
@@ -0,0 +1,37 @@
+/*=============================================================================
+
+    This file is part of ARB.
+
+    ARB is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    ARB is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with ARB; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+=============================================================================*/
+/******************************************************************************
+
+    Copyright (C) 2012 Fredrik Johansson
+
+******************************************************************************/
+
+#include "fmprb.h"
+
+void
+_fmprb_const_log_sqrt2pi(fmprb_t t, long prec)
+{
+    fmprb_const_pi(t, prec + 2);
+    fmprb_mul_2exp_si(t, t, 1);
+    fmprb_log(t, t, prec);
+    fmprb_mul_2exp_si(t, t, -1);
+}
+
+DEF_CACHED_CONSTANT(fmprb_const_log_sqrt2pi, _fmprb_const_log_sqrt2pi)
diff --git a/fmprb/const_pi.c b/fmprb/const_pi.c
index ac31a9df..541f66e1 100644
--- a/fmprb/const_pi.c
+++ b/fmprb/const_pi.c
@@ -25,22 +25,4 @@
 
 #include "fmprb.h"
 
-/* TODO: make  threadsafe; round output */
-
-long fmprb_const_pi_cached_prec = 0;
-fmprb_t fmprb_const_pi_cache;
-
-void
-fmprb_const_pi(fmprb_t x, long prec)
-{
-    if (fmprb_const_pi_cached_prec < prec)
-    {
-        if (fmprb_const_pi_cached_prec == 0)
-            fmprb_init(fmprb_const_pi_cache);
-
-        fmprb_const_pi_chudnovsky(fmprb_const_pi_cache, prec);
-        fmprb_const_pi_cached_prec = prec;
-    }
-
-    fmprb_set_round(x, fmprb_const_pi_cache, prec);
-}
+DEF_CACHED_CONSTANT(fmprb_const_pi, fmprb_const_pi_chudnovsky)
diff --git a/fmprb/gamma.c b/fmprb/gamma.c
index 29c75fbc..5e716f5b 100644
--- a/fmprb/gamma.c
+++ b/fmprb/gamma.c
@@ -54,33 +54,6 @@ bernoulli_cache_compute(long n)
     }
 }
 
-/* log(sqrt(2*pi)) */
-void _fmprb_const_log_sqrt2pi(fmprb_t t, long prec)
-{
-    fmprb_const_pi(t, prec + 2);
-    fmprb_mul_2exp_si(t, t, 1);
-    fmprb_log(t, t, prec);
-    fmprb_mul_2exp_si(t, t, -1);
-}
-
-long fmprb_const_log_sqrt2pi_cached_prec = 0;
-fmprb_t fmprb_const_log_sqrt2pi_cache;
-
-void
-fmprb_const_log_sqrt2pi(fmprb_t x, long prec)
-{  
-    if (fmprb_const_log_sqrt2pi_cached_prec < prec)
-    {
-        if (fmprb_const_log_sqrt2pi_cached_prec == 0)
-            fmprb_init(fmprb_const_log_sqrt2pi_cache);
-
-        _fmprb_const_log_sqrt2pi(fmprb_const_log_sqrt2pi_cache, prec);
-        fmprb_const_log_sqrt2pi_cached_prec = prec;
-    }
-
-    fmprb_set_round(x, fmprb_const_log_sqrt2pi_cache, prec);
-}
-
 double fmpr_get_d(const fmpr_t x)
 {
     double r;