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Simplify calculation of 2^-m in __mpexp
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@ -1,5 +1,10 @@
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2013-01-18 Siddhesh Poyarekar <siddhesh@redhat.com>
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* sysdeps/ieee754/dbl-64/mpa.h (__pow_mp): New function to get an
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mp_no from a power of two.
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* sysdeps/ieee754/dbl-64/mpexp.c (__mpexp): Remove
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__mpexp_twomm1. Use __pow_mp.
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* sysdeps/ieee754/dbl-64/mpexp.c (__mpexp): Remove unnecessary
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multiplication.
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@ -123,3 +123,33 @@ extern void __mpsqrt (mp_no *, mp_no *, int);
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extern void __mpexp (mp_no *, mp_no *, int);
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extern void __c32 (mp_no *, mp_no *, mp_no *, int);
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extern int __mpranred (double, mp_no *, int);
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/* Given a power POW, build a multiprecision number 2^POW. */
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static inline void
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__pow_mp (int pow, mp_no *y, int p)
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{
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int i, rem;
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/* The exponent is E such that E is a factor of 2^24. The remainder (of the
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form 2^x) goes entirely into the first digit of the mantissa as it is
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always less than 2^24. */
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EY = pow / 24;
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rem = pow - EY * 24;
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EY++;
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/* If the remainder is negative, it means that POW was negative since
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|EY * 24| <= |pow|. Adjust so that REM is positive and still less than
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24 because of which, the mantissa digit is less than 2^24. */
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if (rem < 0)
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{
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EY--;
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rem += 24;
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}
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/* The sign of any 2^x is always positive. */
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Y[0] = ONE;
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Y[1] = 1 << rem;
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/* Everything else is ZERO. */
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for (i = 2; i <= p; i++)
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Y[i] = ZERO;
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}
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@ -43,7 +43,7 @@ SECTION
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__mpexp (mp_no *x, mp_no *y, int p)
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{
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int i, j, k, m, m1, m2, n;
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double a, b;
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double b;
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static const int np[33] =
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{
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0, 0, 0, 0, 3, 3, 4, 4, 5, 4, 4, 5, 5, 5, 6, 6, 6, 6, 6, 6,
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@ -61,19 +61,6 @@ __mpexp (mp_no *x, mp_no *y, int p)
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70, 73, 76, 78,
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81
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};
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/* Stored values for 2^-m, where values of m are defined in M1P above. */
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static const double __mpexp_twomm1[33] =
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{
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0x1.0p0, 0x1.0p0, 0x1.0p0, 0x1.0p0,
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0x1.0p-17, 0x1.0p-23, 0x1.0p-23, 0x1.0p-28,
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0x1.0p-27, 0x1.0p-38, 0x1.0p-42, 0x1.0p-39,
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0x1.0p-43, 0x1.0p-47, 0x1.0p-43, 0x1.0p-47,
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0x1.0p-50, 0x1.0p-54, 0x1.0p-57, 0x1.0p-60,
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0x1.0p-64, 0x1.0p-67, 0x1.0p-71, 0x1.0p-74,
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0x1.0p-68, 0x1.0p-71, 0x1.0p-74, 0x1.0p-77,
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0x1.0p-70, 0x1.0p-73, 0x1.0p-76, 0x1.0p-78,
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0x1.0p-81
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};
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static const int m1np[7][18] =
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{
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{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
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@ -98,18 +85,10 @@ __mpexp (mp_no *x, mp_no *y, int p)
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/* Choose m,n and compute a=2**(-m). */
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n = np[p];
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m1 = m1p[p];
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a = __mpexp_twomm1[p];
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for (i = 0; i < EX; i++)
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a *= RADIXI;
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for (; i > EX; i--)
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a *= RADIX;
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b = X[1];
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m2 = 24 * EX;
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for (; b < HALFRAD; m2--)
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{
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a *= TWO;
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b *= TWO;
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}
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b *= TWO;
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if (b == HALFRAD)
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{
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for (i = 2; i <= p; i++)
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@ -118,10 +97,7 @@ __mpexp (mp_no *x, mp_no *y, int p)
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break;
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}
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if (i == p + 1)
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{
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m2--;
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a *= TWO;
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}
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m2--;
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}
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m = m1 + m2;
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@ -134,14 +110,13 @@ __mpexp (mp_no *x, mp_no *y, int p)
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than 2^-55. */
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assert (p < 18);
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m = 0;
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a = ONE;
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for (i = n - 1; i > 0; i--, n--)
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if (m1np[i][p] + m2 > 0)
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break;
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}
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/* Compute s=x*2**(-m). Put result in mps. */
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__dbl_mp (a, &mpt1, p);
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__pow_mp (-m, &mpt1, p);
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__mul (x, &mpt1, &mps, p);
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/* Evaluate the polynomial. Put result in mpt2. */
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