refactored F16 implementation

1 files changed, 42 insertions, 89 deletions

diff --git a/lib/rfxswf.c b/lib/rfxswf.c
index a729f6d7..bba220fd 100644
--- a/lib/rfxswf.c
+++ b/lib/rfxswf.c
@@ -410,115 +410,68 @@ int swf_SetU30String(TAG*tag, const char*str, int l)
 
 float swf_GetF16(TAG * t)
 {
-      U16 f1 = swf_GetU16(t);
-      if(!f1) return 0;
-#if 0
-    // D16 is 1-5-10
-    // D32 is 1-8-23
+    U16 f1 = swf_GetU16(t);
+    if(!(f1&0x3ff)) return 0.0;
+
+    // IEEE 16 is 1-5-10
+    // IEEE 32 is 1-8-23
     /* gcc 4.1.2 seems to require a union here. *(float*)u doesn't work */
     union {
       U32 u;
       float f;
     } f2;
-    f2.u = (f1&0x8000)<<16; //sign
-    f2.u |= ((f1&0x7c00)<<13)+(0x40000000-(0x4000<<13)); //exp
-    f2.u |= (f1&0x03ff)<<13; //mantissa
-    return *(float*)&f2;
-#endif
 
-    double d = (f1 & 32768L) != 1L ? 1.0 : -1.0;
-    int i = (int)((f1 & 0x7c00) >> 10) - 16;
-    double d1 = (double)(f1 & 1023) / 1024.0;
-    //FloatingPointValue floatingpointvalue = new FloatingPointValue(d1, i);
-    double value = d1 * pow(2, i);	
-
-#if 0
-    if(t->id != 0) {
-    TAG*tag = swf_InsertTag(0, 0);
-    //swf_SetF16(tag, value);
-    swf_SetF16(tag, 84.0/1024.0);
-    U16 f = swf_GetU16(tag);
-    tag->pos = 0;
-    fprintf(stderr, "%04x -> %f -> %04x -> %f\n", (int)f1, d*value, f, swf_GetF16(tag)*1024.0);
-    swf_DeleteTag(0,tag);
+    U16 e = (f1>>10)&0x1f;
+    U16 m = f1&0x3ff;
+    /* find highest bit in mantissa */
+    int h=0;
+    while(!(m&0x400)) {
+	m<<=1;
+	h++;
     }
-#endif
+    m&=0x3ff;
+    e -= h;
+    e += 0x6f;
 
-    return (float)(d*value);
+    f2.u = (f1&0x8000)<<16; //sign
+    f2.u |= e<<23; //exponent
+    f2.u |= m<<13; //mantissa
+    return *(float*)&f2;
 }
 
 void swf_SetF16(TAG * t, float f)
 {
-#if 0
-    U32 f1 = *(U32*)&f;
-    U16 f2 = (f1>>16)&0x8000;
-    int exp = ((f1>>23)&0xff)-0x80+0x10;
-    if(exp<0) {
-	if(exp!=(16-128)) {
-	    fprintf(stderr, "Exponent underflow in FLOAT16 encoding %d\n", exp);
-	}
+    union {
+      U32 u;
+      float f;
+    } v;
+    v.f = f;
+
+    U16 result = (v.u>>16)&0x8000; //sign
+    int exp = ((v.u>>23)&0xff)-0x7f+0x10;
+    U16 m = (v.u>>13)&0x3ff;
+    //fprintf(stderr, "%f: %04x sign, %d exp, %04x mantissa\n", f, result, exp, m);
+    if(exp<-10) {
+	// underflow (clamp to 0.0)
+	exp = 0;
+	m = 0;
+    } else if(exp<0) {
+        // partial underflow- strip some bits
+	m = (m|0x400)>>-exp;
 	exp = 0;
     } else if(exp>=32) {
 	exp = 31;
+	m = 0x3ff;
 	fprintf(stderr, "Exponent overflow in FLOAT16 encoding\n");
-    }
-    f2 |= exp<<10;
-    f2 |= (f1>>13)&0x3ff;
-    swf_SetU16(t, f2);
-#endif
-    
-    if(f == 0.0F)
-    {
-	swf_SetU16(t, 0);
-	return;
-    }
-    union {
-	double value;
-	long long l;
-    } x;
-    x.value = (double)f;
-
-    double mantissa;
-    double exp;
-    if(x.value == 0.0)
-    {
-      exp = 0;
-      mantissa = 0.0;
-    } else {
-      union {
-	  double d;
-	  long long l;
-      } u;
-      u.l = (0x800fffffffffffffLL & x.l) | 0x3fe0000000000000LL;
-      mantissa = u.d;
-      exp = (int)(((0x7ff0000000000000LL & x.l) >> 52) - 1022L);
-    }
-
-    double d = mantissa;
-    int i = exp;
-    int j = i + 16;
-    if(j < 0 || j > 31) 
-    {
-	fprintf(stderr, "too large or too small\n");	
-	swf_SetU16(t, 0);
-	return;
-    }
-    U16 p;
-    if(d >= 0.0) {
-	p = 0;
     } else {
-	d *= -1;
-	p = 32768;
+	exp++;
+	m = (m>>1)|0x200;
     }
-    p |= j << 10;
-    p |= (int)(d * 1024);
-
-    //fprintf(stderr, "%f/%f -> %04x\n", mantissa, exp, p);
-
-    swf_SetU16(t, p);
+    result |= exp<<10;
+    result |= m;
+    swf_SetU16(t, result);
 }
 
-
 double swf_GetD64(TAG*tag)
 {
     /* FIXME: this is not big-endian compatible */