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