added: method Big::FromDouble(double) which converts from
standard double into a Big<> (only 32bit platforms) git-svn-id: svn://ttmath.org/publicrep/ttmath/trunk@47 e52654a7-88a9-db11-a3e9-0013d4bc506e
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@ -1682,6 +1682,134 @@ public:
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/*!
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this method converts from standard double into this class
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standard double means IEEE-754 floating point value with 64 bits
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it is as follows (from http://www.psc.edu/general/software/packages/ieee/ieee.html):
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The IEEE double precision floating point standard representation requires
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a 64 bit word, which may be represented as numbered from 0 to 63, left to
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right. The first bit is the sign bit, S, the next eleven bits are the
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exponent bits, 'E', and the final 52 bits are the fraction 'F':
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S EEEEEEEEEEE FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
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0 1 11 12 63
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The value V represented by the word may be determined as follows:
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* If E=2047 and F is nonzero, then V=NaN ("Not a number")
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* If E=2047 and F is zero and S is 1, then V=-Infinity
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* If E=2047 and F is zero and S is 0, then V=Infinity
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* If 0<E<2047 then V=(-1)**S * 2 ** (E-1023) * (1.F) where "1.F" is intended
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to represent the binary number created by prefixing F with an implicit
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leading 1 and a binary point.
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* If E=0 and F is nonzero, then V=(-1)**S * 2 ** (-1022) * (0.F) These are
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"unnormalized" values.
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* If E=0 and F is zero and S is 1, then V=-0
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* If E=0 and F is zero and S is 0, then V=0
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*/
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#ifdef TTMATH_PLATFORM32
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void FromDouble(double value)
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{
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// sizeof(double) should be 8 (64 bits), this is actually not a runtime
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// error but I leave it at the moment as is
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TTMATH_ASSERT( sizeof(double) == 8 )
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// I am not sure what will be on a plaltform which has
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// a different endianness... but we use this library only
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// on x86 and amd (intel) 64 bits (as there's a lot of assembler code)
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union
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{
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double d;
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unsigned int u[2]; // two 32bit words
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} temp;
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temp.d = value;
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info = 0;
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if( temp.u[1] & 0x80000000u )
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SetSign();
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int e = (temp.u[1] & 0x7FF00000u) >> 20;
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unsigned int m1 = ((temp.u[1] & 0xFFFFFu) << 11) | (temp.u[0] >> 21);
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unsigned int m2 = temp.u[0] << 11;
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if( e == 2047 )
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{
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// If E=2047 and F is nonzero, then V=NaN ("Not a number")
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// If E=2047 and F is zero and S is 1, then V=-Infinity
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// If E=2047 and F is zero and S is 0, then V=Infinity
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// at the moment we do not support NaN, -Infinity and +Infinity
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SetZero();
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}
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else
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if( e > 0 )
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{
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// If 0<E<2047 then
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// V=(-1)**S * 2 ** (E-1023) * (1.F)
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// where "1.F" is intended to represent the binary number
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// created by prefixing F with an implicit leading 1 and a binary point.
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FromDouble_SetExpAndMan(e - 1023 - man*TTMATH_BITS_PER_UINT + 1, 0x80000000u, m1, m2);
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// we do not have to call Standardizing() here
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// because the mantissa will have the highest bit set
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}
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else
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{
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// e == 0
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if( m1 != 0 || m2 != 0 )
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{
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// If E=0 and F is nonzero,
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// then V=(-1)**S * 2 ** (-1022) * (0.F)
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// These are "unnormalized" values.
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FromDouble_SetExpAndMan(e - 1022 - man*TTMATH_BITS_PER_UINT + 1, 0, m1, m2);
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Standardizing();
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}
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else
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{
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// If E=0 and F is zero and S is 1, then V=-0
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// If E=0 and F is zero and S is 0, then V=0
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// we do not support -0 or 0, only is one 0
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SetZero();
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}
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}
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}
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void FromDouble_SetExpAndMan(int e, unsigned int mhighest,
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unsigned int m1, unsigned int m2)
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{
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exponent = e;
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if( man > 1 )
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{
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mantissa.table[man-1] = m1 | mhighest;
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mantissa.table[man-2] = m2;
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for(unsigned int i=0 ; i<man-2 ; ++i)
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mantissa.table[i] = 0;
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}
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else
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{
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mantissa.table[0] = m1 | mhighest;
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}
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}
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#endif
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/*!
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/*!
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an operator= for converting 'sint' to this class
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an operator= for converting 'sint' to this class
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*/
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*/
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