TempleOSTS_140317.ISO

Demo/Lectures/FixedPoint.CPP

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+/*
+"Fixed point" means you use integers
+that are scaled by a value.  A common
+example would be using number of pennies
+instead of dollars with a float.
+
+Fixed-point used to be much $TX,"faster",HTML="http://en.wikipedia.org/wiki/X87"$,
+but modern processors do well with
+floats.  It also depends on the compiler
+and my compiler used to do floats poorly.
+It's a little better.
+
+I often use 64-bit ints with upper 32-bits
+as integer and lower 32-bits as fraction.
+
+See $LK,"::/Demo/SubIntAccess.CPP"$ for how
+to access upper or lower 32-bits.
+
+For a complete lst of nonstandard compiler
+features, see $LK,"::/Doc/HolyC.TXT"$.
+
+*/
+
+U0 Main()
+{
+  F64 t0,f_sum=0,f_val;
+  I64 i ,i_sum=0,i_val;
+
+  i_val= 2.0000002 *0x100000000;
+  t0=tS;
+  for (i=1000000000;i;i--)
+    i_sum+=i_val;
+  "Integer Sum:%.9f Time:%7.3fs\n",i_sum/ToF64(0x100000000),tS-t0;
+
+  f_val= 2.0000002;
+  t0=tS;
+  for (i=1000000000;i;i--)
+    f_sum+=f_val;
+  "Float   Sum:%.9f Time:%7.3fs\n",f_sum,tS-t0;
+  NewLine;
+}
+
+U0 DoIt2()
+{
+  I64 i=0x123456789ABCDEF0;
+  "i           =%X\n",i;
+
+  "i&0xFFFFFFFF=%X\n",i&0xFFFFFFFF;
+  "i>>32       =%X\n",i>>32;
+
+/*
+  Standard integer types are declared
+  with a special compiler feature which
+  allows a structure to be accessed as a
+  whole.  That's why the i variable can
+  be accessed normally in addition to
+  structure member access $LK,"I64",A="MN:I64"$.  The actual
+  intrinsic compiler type is U64i.
+
+public U64i union I64
+{
+  I8i i8[8];
+  U8i u8[8];
+  I16 i16[4];
+  U16 u16[4];
+  I32 i32[2];
+  U32 u32[2];
+};
+
+  It's not quite as great as it seems
+  because the compiler decides it cannot
+  place i into a reg, so there is a
+  penalty.
+
+For a complete lst of nonstandard compiler
+features, see $LK,"::/Doc/HolyC.TXT"$.
+
+*/
+
+  "i.u32[0]    =%X\n",i.u32[0];
+  "i.u32[1]    =%X\n",i.u32[1];
+}
+
+CPURep;
+Main;
+DoIt2;
+
+//See $LK,"::/Demo/Lectures/FixedPointAdvanced.CPP"$
+
+
+/*  Program Output$HL,0$$WW+H,1$$FD,1$
+
+8 Cores 2.660GHz
+Integer Sum:2000000199.768689408 Time:	0.787s
+Float	Sum:2000000225.656126208 Time:	3.918s
+
+i	    =123456789ABCDEF0
+i&0xFFFFFFFF=9ABCDEF0
+i>>32	    =12345678
+i.u32[0]    =9ABCDEF0
+i.u32[1]    =12345678
+
+$HL,1$*/