code: plan9front

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games/snes: use 4-point hermite interpolation to resample

This is noticeably better than nearest-neighbor.

--- a/sys/src/games/snes/dsp.c

+++ b/sys/src/games/snes/dsp.c

@@ -49,7 +49,6 @@

 enum { Freq = 44100 };

 static s16int sbuf[2*2000], *sbufp;

-static int stime;

 static int fd;

 void

@@ -61,16 +60,36 @@

 	sbufp = sbuf;

 }

+static int

+hermite(int *x, int t)

+{

+	int y;

+

+	y = (x[0] - x[6]) / 2 + (x[4] - x[2]) * 3 / 2;

+	y = y * t >> 15;

+	y += x[6] - x[4] * 5 / 2 + x[2] * 2 - x[0] / 2;

+	y = y * t >> 15;

+	y += (x[2] - x[6]) / 2;

+	y = y * t >> 15;

+	y += x[4];

+	return y;

+}

+

 static void

 audiosample(s16int *s)

 {

-	stime -= 1<<16;

+	static int x[8], t;

+

+	x[0] = s[0];

+	x[1] = s[1];

 	do {

-		sbufp[0] = s[0];

-		sbufp[1] = s[1];

+		sbufp[0] = hermite(x, t);

+		sbufp[1] = hermite(x + 1, t);

 		sbufp += 2;

-		stime += (32000<<16)/Freq;

-	} while(stime < 0);

+		t += (32000<<15)/Freq;

+	} while(t < 1<<15);

+	t -= 1<<15;

+	memmove(x + 2, x, sizeof(x) - 2 * sizeof(x[0]));

 }

 int