quantization: Add assertions for quantizeFloat N argument

Also convert C comments to C++ - this is no longer part of
meshoptimizer.h so it doesn't need to be C89 compatible.

src/quantization.cpp

@@ -1,6 +1,8 @@
 // This file is part of meshoptimizer library; see meshoptimizer.h for version/license details
 #include "meshoptimizer.h"
 
+#include <assert.h>
+
 unsigned short meshopt_quantizeHalf(float v)
 {
 	union { float f; unsigned int ui; } u = {v};
@@ -9,23 +11,25 @@ unsigned short meshopt_quantizeHalf(float v)
 	int s = (ui >> 16) & 0x8000;
 	int em = ui & 0x7fffffff;
 
-	/* bias exponent and round to nearest; 112 is relative exponent bias (127-15) */
+	// bias exponent and round to nearest; 112 is relative exponent bias (127-15)
 	int h = (em - (112 << 23) + (1 << 12)) >> 13;
 
-	/* underflow: flush to zero; 113 encodes exponent -14 */
+	// underflow: flush to zero; 113 encodes exponent -14
 	h = (em < (113 << 23)) ? 0 : h;
 
-	/* overflow: infinity; 143 encodes exponent 16 */
+	// overflow: infinity; 143 encodes exponent 16
 	h = (em >= (143 << 23)) ? 0x7c00 : h;
 
-	/* NaN; note that we convert all types of NaN to qNaN */
+	// NaN; note that we convert all types of NaN to qNaN
 	h = (em > (255 << 23)) ? 0x7e00 : h;
 
 	return (unsigned short)(s | h);
 }
 
 float meshopt_quantizeFloat(float v, int N)
 {
+	assert(N >= 0 && N <= 23);
+
 	union { float f; unsigned int ui; } u = {v};
 	unsigned int ui = u.ui;
 
@@ -35,10 +39,10 @@ float meshopt_quantizeFloat(float v, int N)
 	int e = ui & 0x7f800000;
 	unsigned int rui = (ui + round) & ~mask;
 
-	/* round all numbers except inf/nan; this is important to make sure nan doesn't overflow into -0 */
+	// round all numbers except inf/nan; this is important to make sure nan doesn't overflow into -0
 	ui = e == 0x7f800000 ? ui : rui;
 
-	/* flush denormals to zero */
+	// flush denormals to zero
 	ui = e == 0 ? 0 : ui;
 
 	u.ui = ui;