From 7722705676a8c7d52c612057de241167459b9e33 Mon Sep 17 00:00:00 2001
From: Fred Wright <fw@fwright.net>
Date: Wed, 13 Mar 2019 19:37:33 -0700
Subject: Avoids troublesome dependency on M_LN2 from math.h.

The M_LN2 definition isn't always provided by math.h, depending on the
settings of the pesky configure flags.  Since ln(2) is a mathematical
constant, there's no loss of generality in defining our own version,
and that decouples us from the variability.

Since the stated purpose of defining _XOPEN_SOURCE in driver_tsip.c
and driver_zodiac.c is just to make M_LN2 available, this is
no longer necessary.

TESTED:
(With subsequent fixes included) Ran "build-all check" on Mac Pro
10.9, Mac Pro 10.14, MacBook Pro 10.9, PowerBook 10.5, VMs for OSX
10.5-10.13, Ubuntu 14.04, CentOS 7, Fedora 25, FreeBSD 10.3, OpenBSD
5.6, OpenBSD 5.6 32-bit, NetBSD 6.1.5, and Beaglebone (arm) Debian 7.
---
 driver_tsip.c   |  9 +--------
 driver_zodiac.c | 10 +---------
 gps.h           |  4 ++++
 3 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/driver_tsip.c b/driver_tsip.c
index 55010584..0add16ba 100644
--- a/driver_tsip.c
+++ b/driver_tsip.c
@@ -13,13 +13,6 @@
  * SPDX-License-Identifier: BSD-2-clause
  */
 
-#ifdef __linux__
-/* FreeBSD chokes on this */
-/* if we insist on C99, then we need this to get M_LN2 from math.h */
-/* 500 mean X/Open 1995 */
-#define _XOPEN_SOURCE 500
-#endif /* __linux__ */
-
 #if !defined(_POSIX_C_SOURCE) || _POSIX_C_SOURCE < 200112L
 /* round() needs  _POSIX_C_SOURCE >= 200112L */
 #define  _POSIX_C_SOURCE 200112L
@@ -1186,7 +1179,7 @@ static bool tsip_speed_switch(struct gps_device_t *session,
     }
 
     putbyte(buf, 0, 0xff);	/* current port */
-    putbyte(buf, 1, (round(log((double)speed / 300) / M_LN2)) + 2);	/* input dev.baudrate */
+    putbyte(buf, 1, (round(log((double)speed / 300) / GPS_LN2)) + 2);	/* input dev.baudrate */
     putbyte(buf, 2, getub(buf, 1));	/* output baudrate */
     putbyte(buf, 3, 3);		/* character width (8 bits) */
     putbyte(buf, 4, parity);	/* parity (normally odd) */
diff --git a/driver_zodiac.c b/driver_zodiac.c
index b4c38b01..41a5565a 100644
--- a/driver_zodiac.c
+++ b/driver_zodiac.c
@@ -10,14 +10,6 @@
  * SPDX-License-Identifier: BSD-2-clause
  */
 
-#ifdef __linux__
-/* FreeBSD chokes on this */
-/* if we insist on C99, then we need this to get M_LN2 from math.h */
-/* if we insisnt on C99, then we need this to get M_LN2 from math.h */
-/* 500 means X/Open 1995 */
-#define _XOPEN_SOURCE 500
-#endif /* __linux__ */
-
 #if !defined(_POSIX_C_SOURCE) || _POSIX_C_SOURCE < 200112L
 /* round() needs  _POSIX_C_SOURCE >= 200112L */
 #define  _POSIX_C_SOURCE 200112L
@@ -447,7 +439,7 @@ static bool zodiac_speed_switch(struct gps_device_t *session,
     data[2] = (unsigned short)parity;	/* port 1 character width (8 bits) */
     data[3] = (unsigned short)(stopbits - 1);	/* port 1 stop bits (1 stopbit) */
     data[4] = 0;		/* port 1 parity (none) */
-    data[5] = (unsigned short)(round(log((double)speed / 300) / M_LN2) + 1);	/* port 1 speed */
+    data[5] = (unsigned short)(round(log((double)speed / 300) / GPS_LN2) + 1);	/* port 1 speed */
     data[14] = zodiac_checksum(data, 14);
 
     (void)zodiac_spew(session, 1330, data, 15);
diff --git a/gps.h b/gps.h
index 35404615..23a97594 100644
--- a/gps.h
+++ b/gps.h
@@ -2240,6 +2240,10 @@ extern double wgs84_separation(double, double);
 #define RAD_2_DEG	57.2957795130823208767981548141051703
 #define DEG_2_RAD	0.0174532925199432957692369076848861271
 
+/* other mathematical constants */
+#define GPS_LN2         0.693147180559945309417232121458176568
+
+
 /* geodetic constants */
 #define WGS84A 6378137		/* equatorial radius */
 #define WGS84F 298.257223563	/* flattening */
-- 
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