50 lines
895 B
C
50 lines
895 B
C
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/* catan.c */
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/*
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Contributed by Danny Smith
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2003-10-17
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FIXME: This needs some serious numerical analysis.
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*/
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#include <math.h>
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#include <complex.h>
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#include <errno.h>
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/* catan (z) = -I/2 * clog ((I + z) / (I - z)) */
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double complex
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catan (double complex Z)
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{
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double complex Res;
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double complex Tmp;
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double x = __real__ Z;
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double y = __imag__ Z;
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if ( x == 0.0 && (1.0 - fabs (y)) == 0.0)
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{
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errno = ERANGE;
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__real__ Res = HUGE_VAL;
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__imag__ Res = HUGE_VAL;
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}
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else if (isinf (_hypot (x, y)))
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{
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__real__ Res = (x > 0 ? M_PI_2 : -M_PI_2);
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__imag__ Res = 0.0;
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}
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else
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{
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__real__ Tmp = - x;
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__imag__ Tmp = 1.0 - y;
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__real__ Res = x;
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__imag__ Res = y + 1.0;
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Tmp = clog (Res/Tmp);
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__real__ Res = - 0.5 * __imag__ Tmp;
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__imag__ Res = 0.5 * __real__ Tmp;
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}
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return Res;
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}
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