replay_gain_info, ...: use cmath instead of math.h in C++ mode

Fixes build problems with mingw32.

src/CrossFade.cxx

@@ -23,6 +23,8 @@
 #include "audio_format.h"
 #include "tag.h"
 
+#include <cmath>
+
 #include <assert.h>
 #include <string.h>
 #include <stdlib.h>
@@ -82,9 +84,8 @@ static float mixramp_interpolate(char *ramp_list, float required_db)
 		}
 
 		/* If required db < any stored value, use the least. */
-		if (isnan(last_db)) {
+		if (std::isnan(last_db))
 			return secs;
-		}
 
 		/* Finally, interpolate linearly. */
 		secs = last_secs + (required_db - last_db) * (secs - last_secs) / (db - last_db);
@@ -114,13 +115,14 @@ unsigned cross_fade_calc(float duration, float total_time,
 
 	chunks_f = (float)audio_format_time_to_size(af) / (float)CHUNK_SIZE;
 
-	if (isnan(mixramp_delay) || !(mixramp_start) || !(mixramp_prev_end)) {
+	if (std::isnan(mixramp_delay) || !mixramp_start || !mixramp_prev_end) {
 		chunks = (chunks_f * duration + 0.5);
 	} else {
 		/* Calculate mixramp overlap. */
 		mixramp_overlap = mixramp_interpolate(mixramp_start, mixramp_db - replay_gain_db)
 		  + mixramp_interpolate(mixramp_prev_end, mixramp_db - replay_gain_prev_db);
-		if (!isnan(mixramp_overlap) && (mixramp_delay <= mixramp_overlap)) {
+		if (!std::isnan(mixramp_overlap) &&
+		    mixramp_delay <= mixramp_overlap) {
 			chunks = (chunks_f * (mixramp_overlap - mixramp_delay));
 			g_debug("will overlap %d chunks, %fs", chunks,
 				mixramp_overlap - mixramp_delay);

src/PlayerControl.cxx

@@ -28,9 +28,10 @@ extern "C" {
 #include "DecoderControl.hxx"
 #include "Main.hxx"
 
+#include <cmath>
+
 #include <assert.h>
 #include <stdio.h>
-#include <math.h>
 
 static void
 pc_enqueue_song_locked(struct player_control *pc, struct song *song);
@@ -49,7 +50,7 @@ player_control::player_control(unsigned _buffer_chunks,
 	 next_song(nullptr),
 	 cross_fade_seconds(0),
 	 mixramp_db(0),
-	 mixramp_delay_seconds(nanf("")),
+	 mixramp_delay_seconds(std::nanf("")),
 	 total_play_time(0)
 {
 }

src/PlayerThread.cxx

@@ -37,6 +37,8 @@ extern "C" {
 #include "idle.h"
 }
 
+#include <cmath>
+
 #include <glib.h>
 
 #undef G_LOG_DOMAIN
@@ -759,7 +761,7 @@ play_next_chunk(struct player *player)
 						  other_chunk->tag);
 			other_chunk->tag = NULL;
 
-			if (isnan(pc->mixramp_delay_seconds)) {
+			if (std::isnan(pc->mixramp_delay_seconds)) {
 				chunk->mix_ratio = ((float)cross_fade_position)
 					     / player->cross_fade_chunks;
 			} else {

src/ReplayGainConfig.cxx

@@ -33,7 +33,6 @@ extern "C" {
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
-#include <math.h>
 
 enum replay_gain_mode replay_gain_mode = REPLAY_GAIN_OFF;
 

src/replay_gain_info.h

@@ -22,8 +22,12 @@
 
 #include "check.h"
 
+#ifdef __cplusplus
+#include <cmath>
+#else
 #include <stdbool.h>
 #include <math.h>
+#endif
 
 enum replay_gain_mode {
 	REPLAY_GAIN_AUTO = -2,
@@ -58,7 +62,11 @@ replay_gain_info_init(struct replay_gain_info *info)
 static inline bool
 replay_gain_tuple_defined(const struct replay_gain_tuple *tuple)
 {
+#ifdef __cplusplus
+	return !std::isinf(tuple->gain);
+#else
 	return !isinf(tuple->gain);
+#endif
 }
 
 #ifdef __cplusplus