add mag_get_d_log2_approx as a public method

acb_hypgeom/pfq_choose_n.c

@@ -11,8 +11,6 @@
 
 #include "acb_hypgeom.h"
 
-double mag_get_log2_d_approx(const mag_t x);
-
 #define D_ABS(x) ((x) < 0.0 ? (-(x)) : (x))
 
 int
@@ -108,7 +106,7 @@ acb_hypgeom_pfq_choose_n_max(acb_srcptr a, slong p,
     bim = bre + q;
 
     acb_get_mag(zmag, z);
-    log2_z = mag_get_log2_d_approx(zmag);
+    log2_z = mag_get_d_log2_approx(zmag);
 
     n_skip = 1;
     n_min = 1;
@@ -217,7 +215,7 @@ acb_hypgeom_pfq_series_choose_n(const acb_poly_struct * a, slong p,
     bim = bre + q;
 
     acb_get_mag(zmag, z->coeffs);
-    log2_z = mag_get_log2_d_approx(zmag);
+    log2_z = mag_get_d_log2_approx(zmag);
 
     n_skip = 1;
     n_min = 1;

acb_modular/eta_sum.c

@@ -11,8 +11,6 @@
 
 #include "acb_modular.h"
 
-double mag_get_log2_d_approx(const mag_t x);
-
 static const int pentagonal_best_m[] = {
   2, 5, 7, 11, 13, 17, 19, 23, 25, 35,
   55, 65, 77, 91, 119, 133, 143, 175, 275, 325,
@@ -227,7 +225,7 @@ acb_modular_eta_sum(acb_t eta, const acb_t q, slong prec)
     q_is_real = arb_is_zero(acb_imagref(q));
 
     acb_get_mag(qmag, q);
-    log2q_approx = mag_get_log2_d_approx(qmag);
+    log2q_approx = mag_get_d_log2_approx(qmag);
 
     if (log2q_approx >= 0.0)
     {

acb_modular/theta_const_sum.c

@@ -11,8 +11,6 @@
 
 #include "acb_modular.h"
 
-double mag_get_log2_d_approx(const mag_t x);
-
 void
 acb_modular_theta_const_sum(acb_t theta2, acb_t theta3, acb_t theta4,
     const acb_t q, slong prec)
@@ -26,7 +24,7 @@ acb_modular_theta_const_sum(acb_t theta2, acb_t theta3, acb_t theta4,
     mag_init(err);
 
     acb_get_mag(qmag, q);
-    log2q_approx = mag_get_log2_d_approx(qmag);
+    log2q_approx = mag_get_d_log2_approx(qmag);
 
     is_real = arb_is_zero(acb_imagref(q));
     is_real_or_imag = is_real || arb_is_zero(acb_realref(q));

acb_modular/theta_const_sum_basecase.c

@@ -11,8 +11,6 @@
 
 #include "acb_modular.h"
 
-double mag_get_log2_d_approx(const mag_t x);
-
 void
 acb_modular_theta_const_sum_basecase(acb_t theta2, acb_t theta3, acb_t theta4,
     const acb_t q, slong N, slong prec)
@@ -125,7 +123,7 @@ acb_modular_theta_const_sum_basecase(acb_t theta2, acb_t theta3, acb_t theta4,
     acb_modular_fill_addseq(tab, N);
 
     acb_get_mag(qmag, q);
-    log2q_approx = mag_get_log2_d_approx(qmag);
+    log2q_approx = mag_get_d_log2_approx(qmag);
 
     for (k = 0; k < N; k++)
     {

acb_modular/theta_const_sum_rs.c

@@ -11,8 +11,6 @@
 
 #include "acb_modular.h"
 
-double mag_get_log2_d_approx(const mag_t x);
-
 static const int square_best_m[] = {
   2, 3, 4, 8, 12, 16, 32, 48, 80, 96, 
   112, 144, 240, 288, 336, 480, 560, 576, 720, 1008, 
@@ -95,7 +93,7 @@ acb_modular_theta_const_sum_rs(acb_t theta2, acb_t theta3, acb_t theta4,
 
     mag_init(qmag);
     acb_get_mag(qmag, q);
-    log2q_approx = mag_get_log2_d_approx(qmag);
+    log2q_approx = mag_get_d_log2_approx(qmag);
     mag_clear(qmag);
 
     acb_init(tmp1);

acb_modular/theta_sum.c

@@ -11,36 +11,6 @@
 
 #include "acb_modular.h"
 
-double
-mag_get_log2_d_approx(const mag_t x)
-{
-    if (mag_is_zero(x))
-    {
-        return COEFF_MIN;
-    }
-    else if (mag_is_inf(x))
-    {
-        return COEFF_MAX;
-    }
-    else if (COEFF_IS_MPZ(MAG_EXP(x)))
-    {
-        if (fmpz_sgn(MAG_EXPREF(x)) < 0)
-            return COEFF_MIN;
-        else
-            return COEFF_MAX;
-    }
-    else
-    {
-        slong e = MAG_EXP(x);
-
-        if (e < -20 || e > 20)
-            return e;
-        else
-            return e + 1.4426950408889634074 *
-                mag_d_log_upper_bound(MAG_MAN(x) * ldexp(1.0, -MAG_BITS));
-    }
-}
-
 void
 acb_modular_theta_sum(acb_ptr theta1,
                           acb_ptr theta2,
@@ -84,7 +54,7 @@ acb_modular_theta_sum(acb_ptr theta1,
         acb_inv(v, w, prec);
 
     acb_get_mag(qmag, q);
-    log2q_approx = mag_get_log2_d_approx(qmag);
+    log2q_approx = mag_get_d_log2_approx(qmag);
 
     if (w_is_unit)
     {
@@ -97,7 +67,7 @@ acb_modular_theta_sum(acb_ptr theta1,
         acb_get_mag(wmag, w);
         acb_get_mag(vmag, v);
         mag_max(wmag, wmag, vmag);
-        log2w_approx = mag_get_log2_d_approx(wmag);
+        log2w_approx = mag_get_d_log2_approx(wmag);
     }
 
     if (log2q_approx >= 0.0)

doc/source/mag.rst

@@ -175,6 +175,12 @@ Conversions
 
     Returns a *double* giving an upper bound for *x*.
 
+.. function:: double mag_get_d_log2_approx(const mag_t x)
+
+    Returns a *double* approximating `\log_2(x)`, suitable for estimating
+    magnitudes (not for rigorous bounds).
+    The value is clamped between COEFF_MIN and COEFF_MAX.
+
 .. function:: void mag_set_ui_lower(mag_t z, ulong x)
 
 .. function:: void mag_set_fmpz_lower(mag_t z, const fmpz_t x)

mag.h

@@ -546,6 +546,8 @@ MAG_INLINE void mag_set_d(mag_t z, double x)
 
 double mag_get_d(const mag_t z);
 
+double mag_get_d_log2_approx(const mag_t x);
+
 /* TODO: document */
 double mag_d_log_upper_bound(double x);
 double mag_d_log_lower_bound(double x);

mag/get_d_log2_approx.c

@@ -0,0 +1,43 @@
+/*
+    Copyright (C) 2014 Fredrik Johansson
+
+    This file is part of Arb.
+
+    Arb is free software: you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 2.1 of the License, or
+    (at your option) any later version.  See <http://www.gnu.org/licenses/>.
+*/
+
+#include "mag.h"
+
+double
+mag_get_d_log2_approx(const mag_t x)
+{
+    if (mag_is_zero(x))
+    {
+        return COEFF_MIN;
+    }
+    else if (mag_is_inf(x))
+    {
+        return COEFF_MAX;
+    }
+    else if (COEFF_IS_MPZ(MAG_EXP(x)))
+    {
+        if (fmpz_sgn(MAG_EXPREF(x)) < 0)
+            return COEFF_MIN;
+        else
+            return COEFF_MAX;
+    }
+    else
+    {
+        slong e = MAG_EXP(x);
+
+        if (e < -20 || e > 20)
+            return e;
+        else
+            return e + 1.4426950408889634074 *
+                mag_d_log_upper_bound(MAG_MAN(x) * ldexp(1.0, -MAG_BITS));
+    }
+}
+