ALSA: refine rate selection in snd_interval_ratnum()

Refine the rate selection by choosing the rate
closer to the requested one in case of selecting
single frequency. Previously, the higher rate was
always selected.

Also, fix problem with the best_diff unsigned int
value wrapping (turning negative).

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_lib.c

@@ -745,10 +745,13 @@ int snd_interval_ratnum(struct snd_interval *i,
 			unsigned int rats_count, struct snd_ratnum *rats,
 			unsigned int *nump, unsigned int *denp)
 {
-	unsigned int best_num, best_diff, best_den;
+	unsigned int best_num, best_den;
+	int best_diff;
 	unsigned int k;
 	struct snd_interval t;
 	int err;
+	unsigned int result_num, result_den;
+	int result_diff;
 
 	best_num = best_den = best_diff = 0;
 	for (k = 0; k < rats_count; ++k) {
@@ -770,6 +773,8 @@ int snd_interval_ratnum(struct snd_interval *i,
 				den -= r;
 		}
 		diff = num - q * den;
+		if (diff < 0)
+			diff = -diff;
 		if (best_num == 0 ||
 		    diff * best_den < best_diff * den) {
 			best_diff = diff;
@@ -784,6 +789,9 @@ int snd_interval_ratnum(struct snd_interval *i,
 	t.min = div_down(best_num, best_den);
 	t.openmin = !!(best_num % best_den);
 	
+	result_num = best_num;
+	result_diff = best_diff;
+	result_den = best_den;
 	best_num = best_den = best_diff = 0;
 	for (k = 0; k < rats_count; ++k) {
 		unsigned int num = rats[k].num;
@@ -806,6 +814,8 @@ int snd_interval_ratnum(struct snd_interval *i,
 				den += rats[k].den_step - r;
 		}
 		diff = q * den - num;
+		if (diff < 0)
+			diff = -diff;
 		if (best_num == 0 ||
 		    diff * best_den < best_diff * den) {
 			best_diff = diff;
@@ -825,10 +835,14 @@ int snd_interval_ratnum(struct snd_interval *i,
 		return err;
 
 	if (snd_interval_single(i)) {
+		if (best_diff * result_den < result_diff * best_den) {
+			result_num = best_num;
+			result_den = best_den;
+		}
 		if (nump)
-			*nump = best_num;
+			*nump = result_num;
 		if (denp)
-			*denp = best_den;
+			*denp = result_den;
 	}
 	return err;
 }