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Diffstat (limited to 'gnu/lib/libgmp/mpq/get_d.c')
| -rw-r--r-- | gnu/lib/libgmp/mpq/get_d.c | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/gnu/lib/libgmp/mpq/get_d.c b/gnu/lib/libgmp/mpq/get_d.c new file mode 100644 index 00000000000..cb4e800d381 --- /dev/null +++ b/gnu/lib/libgmp/mpq/get_d.c @@ -0,0 +1,151 @@ +/* double mpq_get_d (mpq_t src) -- Return the double approximation to SRC. + +Copyright (C) 1995, 1996 Free Software Foundation, Inc. + +This file is part of the GNU MP Library. + +The GNU MP Library is free software; you can redistribute it and/or modify +it under the terms of the GNU Library General Public License as published by +the Free Software Foundation; either version 2 of the License, or (at your +option) any later version. + +The GNU MP Library is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public +License for more details. + +You should have received a copy of the GNU Library General Public License +along with the GNU MP Library; see the file COPYING.LIB. If not, write to +the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, +MA 02111-1307, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" +#include "longlong.h" + +/* Algorithm: + 1. Develop >= n bits of src.num / src.den, where n is the number of bits + in a double. This (partial) division will use all bits from the + denominator. + 2. Use the remainder to determine how to round the result. + 3. Assign the integral result to a temporary double. + 4. Scale the temporary double, and return the result. + + An alternative algorithm, that would be faster: + 0. Let n be somewhat larger than the number of significant bits in a double. + 1. Extract the most significant n bits of the denominator, and an equal + number of bits from the numerator. + 2. Interpret the extracted numbers as integers, call them a and b + respectively, and develop n bits of the fractions ((a + 1) / b) and + (a / (b + 1)) using mpn_divrem. + 3. If the computed values are identical UP TO THE POSITION WE CARE ABOUT, + we are done. If they are different, repeat the algorithm from step 1, + but first let n = n * 2. + 4. If we end up using all bits from the numerator and denominator, fall + back to the first algorithm above. + 5. Just to make life harder, The computation of a + 1 and b + 1 above + might give carry-out... Needs special handling. It might work to + subtract 1 in both cases instead. +*/ + +double +#if __STDC__ +mpq_get_d (const MP_RAT *src) +#else +mpq_get_d (src) + const MP_RAT *src; +#endif +{ + mp_ptr np, dp; + mp_ptr rp; + mp_size_t nsize = src->_mp_num._mp_size; + mp_size_t dsize = src->_mp_den._mp_size; + mp_size_t qsize, rsize; + mp_size_t sign_quotient = nsize ^ dsize; + unsigned normalization_steps; + mp_limb_t qlimb; +#define N_QLIMBS (1 + (sizeof (double) + BYTES_PER_MP_LIMB-1) / BYTES_PER_MP_LIMB) + mp_limb_t qp[N_QLIMBS + 1]; + TMP_DECL (marker); + + if (nsize == 0) + return 0.0; + + TMP_MARK (marker); + nsize = ABS (nsize); + dsize = ABS (dsize); + np = src->_mp_num._mp_d; + dp = src->_mp_den._mp_d; + + rsize = dsize + N_QLIMBS; + rp = (mp_ptr) TMP_ALLOC ((rsize + 1) * BYTES_PER_MP_LIMB); + + count_leading_zeros (normalization_steps, dp[dsize - 1]); + + /* Normalize the denominator, i.e. make its most significant bit set by + shifting it NORMALIZATION_STEPS bits to the left. Also shift the + numerator the same number of steps (to keep the quotient the same!). */ + if (normalization_steps != 0) + { + mp_ptr tp; + mp_limb_t nlimb; + + /* Shift up the denominator setting the most significant bit of + the most significant limb. Use temporary storage not to clobber + the original contents of the denominator. */ + tp = (mp_ptr) TMP_ALLOC (dsize * BYTES_PER_MP_LIMB); + mpn_lshift (tp, dp, dsize, normalization_steps); + dp = tp; + + if (rsize > nsize) + { + MPN_ZERO (rp, rsize - nsize); + nlimb = mpn_lshift (rp + (rsize - nsize), + np, nsize, normalization_steps); + } + else + { + nlimb = mpn_lshift (rp, np + (nsize - rsize), + rsize, normalization_steps); + } + if (nlimb != 0) + { + rp[rsize] = nlimb; + rsize++; + } + } + else + { + if (rsize > nsize) + { + MPN_ZERO (rp, rsize - nsize); + MPN_COPY (rp + (rsize - nsize), np, nsize); + } + else + { + MPN_COPY (rp, np + (nsize - rsize), rsize); + } + } + + qlimb = mpn_divmod (qp, rp, rsize, dp, dsize); + qsize = rsize - dsize; + if (qlimb) + { + qp[qsize] = qlimb; + qsize++; + } + + { + double res; + mp_size_t i; + + res = qp[qsize - 1]; + for (i = qsize - 2; i >= 0; i--) + res = res * MP_BASE_AS_DOUBLE + qp[i]; + + res = __gmp_scale2 (res, BITS_PER_MP_LIMB * (nsize - dsize - N_QLIMBS)); + + TMP_FREE (marker); + return sign_quotient >= 0 ? res : -res; + } +} |