From a222292e68fae7c7b7ca9ce1af94aaaf031ad070 Mon Sep 17 00:00:00 2001
From: John Emmas <john@creativepost.co.uk>
Date: Wed, 5 May 2021 17:50:41 +0100
Subject: [PATCH] Emulate exp2f() for older MS compilers where it wasn't
 available

---
 libs/pbd/msvc/msvc_pbd.cc                 | 18 ++++++++++++++++++
 libs/pbd/pbd/msvc_pbd.h                   |  3 ++-
 msvc_extra_headers/ardourext/misc.h.input |  3 ++-
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/libs/pbd/msvc/msvc_pbd.cc b/libs/pbd/msvc/msvc_pbd.cc
index 4d276eb85c..730672a31d 100644
--- a/libs/pbd/msvc/msvc_pbd.cc
+++ b/libs/pbd/msvc/msvc_pbd.cc
@@ -242,6 +242,24 @@ expm1(double x)
 	return (exp(x) - (double)1.0);
 }
 
+//***************************************************************
+//
+//	exp2f()
+//
+// Emulates C99 exp2f() using powf().
+//
+//	Returns:
+//
+//    On Success: 2 raised to the power of 'x'
+//    On Failure: None, except that calling powf(x) should generate
+//                an appropriate error for us (such as INF etc).
+//
+LIBPBD_API float PBD_APICALLTYPE
+exp2f(float x)
+{
+	return (powf(2.0f, x));
+}
+
 //***************************************************************
 //
 //	log1p()
diff --git a/libs/pbd/pbd/msvc_pbd.h b/libs/pbd/pbd/msvc_pbd.h
index f717047c65..d631e5532c 100644
--- a/libs/pbd/pbd/msvc_pbd.h
+++ b/libs/pbd/pbd/msvc_pbd.h
@@ -172,9 +172,10 @@ LIBPBD_API ssize_t  PBD_APICALLTYPE pread(int handle, void *buf, size_t nbytes,
 LIBPBD_API ssize_t  PBD_APICALLTYPE pwrite(int handle, const void *buf, size_t nbytes, off_t offset);
 
 #if defined(_MSC_VER) && (_MSC_VER < 1800)
-LIBPBD_API double   PBD_APICALLTYPE expm1(double x);
 LIBPBD_API double   PBD_APICALLTYPE log1p(double x);
 LIBPBD_API double   PBD_APICALLTYPE round(double x);
+LIBPBD_API double   PBD_APICALLTYPE expm1(double x);
+LIBPBD_API float    PBD_APICALLTYPE exp2f(float x);
 LIBPBD_API float    PBD_APICALLTYPE roundf(float x);
 #endif
 
diff --git a/msvc_extra_headers/ardourext/misc.h.input b/msvc_extra_headers/ardourext/misc.h.input
index 7471ccd649..497224a556 100644
--- a/msvc_extra_headers/ardourext/misc.h.input
+++ b/msvc_extra_headers/ardourext/misc.h.input
@@ -272,9 +272,10 @@ inline int64_t abs(int64_t val) throw()
 // Emulate some C99 math functions which MSVC itself didn't
 // implement until later in life.
 #if defined(_MSC_VER) && (_MSC_VER < 1800)
-extern  double expm1(double x);
 extern  double log1p(double x);
 extern  double round(double x);
+extern  double expm1(double x);
+extern  float  exp2f(float x);
 extern  float roundf(float x);
 #endif
 #if defined(_MSC_VER) && (_MSC_VER < 1900)