223 lines
7 KiB
C
223 lines
7 KiB
C
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/*---------------------------------------------------------------------------+
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| poly_tan.c |
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| Compute the tan of a FPU_REG, using a polynomial approximation. |
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| Copyright (C) 1992,1993,1994,1997,1999 |
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| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, |
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| Australia. E-mail billm@melbpc.org.au |
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+---------------------------------------------------------------------------*/
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#include "exception.h"
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#include "reg_constant.h"
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#include "fpu_emu.h"
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#include "fpu_system.h"
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#include "control_w.h"
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#include "poly.h"
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#define HiPOWERop 3 /* odd poly, positive terms */
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static const unsigned long long oddplterm[HiPOWERop] =
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{
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0x0000000000000000LL,
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0x0051a1cf08fca228LL,
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0x0000000071284ff7LL
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};
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#define HiPOWERon 2 /* odd poly, negative terms */
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static const unsigned long long oddnegterm[HiPOWERon] =
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{
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0x1291a9a184244e80LL,
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0x0000583245819c21LL
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};
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#define HiPOWERep 2 /* even poly, positive terms */
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static const unsigned long long evenplterm[HiPOWERep] =
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{
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0x0e848884b539e888LL,
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0x00003c7f18b887daLL
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};
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#define HiPOWERen 2 /* even poly, negative terms */
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static const unsigned long long evennegterm[HiPOWERen] =
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{
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0xf1f0200fd51569ccLL,
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0x003afb46105c4432LL
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};
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static const unsigned long long twothirds = 0xaaaaaaaaaaaaaaabLL;
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/*--- poly_tan() ------------------------------------------------------------+
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+---------------------------------------------------------------------------*/
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void poly_tan(FPU_REG *st0_ptr)
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{
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long int exponent;
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int invert;
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Xsig argSq, argSqSq, accumulatoro, accumulatore, accum,
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argSignif, fix_up;
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unsigned long adj;
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exponent = exponent(st0_ptr);
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#ifdef PARANOID
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if ( signnegative(st0_ptr) ) /* Can't hack a number < 0.0 */
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{ arith_invalid(0); return; } /* Need a positive number */
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#endif /* PARANOID */
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/* Split the problem into two domains, smaller and larger than pi/4 */
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if ( (exponent == 0) || ((exponent == -1) && (st0_ptr->sigh > 0xc90fdaa2)) )
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{
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/* The argument is greater than (approx) pi/4 */
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invert = 1;
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accum.lsw = 0;
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XSIG_LL(accum) = significand(st0_ptr);
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if ( exponent == 0 )
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{
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/* The argument is >= 1.0 */
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/* Put the binary point at the left. */
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XSIG_LL(accum) <<= 1;
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}
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/* pi/2 in hex is: 1.921fb54442d18469 898CC51701B839A2 52049C1 */
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XSIG_LL(accum) = 0x921fb54442d18469LL - XSIG_LL(accum);
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/* This is a special case which arises due to rounding. */
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if ( XSIG_LL(accum) == 0xffffffffffffffffLL )
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{
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FPU_settag0(TAG_Valid);
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significand(st0_ptr) = 0x8a51e04daabda360LL;
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setexponent16(st0_ptr, (0x41 + EXTENDED_Ebias) | SIGN_Negative);
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return;
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}
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argSignif.lsw = accum.lsw;
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XSIG_LL(argSignif) = XSIG_LL(accum);
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exponent = -1 + norm_Xsig(&argSignif);
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}
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else
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{
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invert = 0;
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argSignif.lsw = 0;
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XSIG_LL(accum) = XSIG_LL(argSignif) = significand(st0_ptr);
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if ( exponent < -1 )
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{
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/* shift the argument right by the required places */
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if ( FPU_shrx(&XSIG_LL(accum), -1-exponent) >= 0x80000000U )
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XSIG_LL(accum) ++; /* round up */
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}
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}
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XSIG_LL(argSq) = XSIG_LL(accum); argSq.lsw = accum.lsw;
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mul_Xsig_Xsig(&argSq, &argSq);
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XSIG_LL(argSqSq) = XSIG_LL(argSq); argSqSq.lsw = argSq.lsw;
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mul_Xsig_Xsig(&argSqSq, &argSqSq);
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/* Compute the negative terms for the numerator polynomial */
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accumulatoro.msw = accumulatoro.midw = accumulatoro.lsw = 0;
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polynomial_Xsig(&accumulatoro, &XSIG_LL(argSqSq), oddnegterm, HiPOWERon-1);
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mul_Xsig_Xsig(&accumulatoro, &argSq);
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negate_Xsig(&accumulatoro);
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/* Add the positive terms */
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polynomial_Xsig(&accumulatoro, &XSIG_LL(argSqSq), oddplterm, HiPOWERop-1);
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/* Compute the positive terms for the denominator polynomial */
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accumulatore.msw = accumulatore.midw = accumulatore.lsw = 0;
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polynomial_Xsig(&accumulatore, &XSIG_LL(argSqSq), evenplterm, HiPOWERep-1);
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mul_Xsig_Xsig(&accumulatore, &argSq);
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negate_Xsig(&accumulatore);
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/* Add the negative terms */
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polynomial_Xsig(&accumulatore, &XSIG_LL(argSqSq), evennegterm, HiPOWERen-1);
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/* Multiply by arg^2 */
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mul64_Xsig(&accumulatore, &XSIG_LL(argSignif));
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mul64_Xsig(&accumulatore, &XSIG_LL(argSignif));
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/* de-normalize and divide by 2 */
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shr_Xsig(&accumulatore, -2*(1+exponent) + 1);
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negate_Xsig(&accumulatore); /* This does 1 - accumulator */
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/* Now find the ratio. */
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if ( accumulatore.msw == 0 )
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{
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/* accumulatoro must contain 1.0 here, (actually, 0) but it
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really doesn't matter what value we use because it will
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have negligible effect in later calculations
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*/
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XSIG_LL(accum) = 0x8000000000000000LL;
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accum.lsw = 0;
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}
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else
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{
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div_Xsig(&accumulatoro, &accumulatore, &accum);
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}
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/* Multiply by 1/3 * arg^3 */
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mul64_Xsig(&accum, &XSIG_LL(argSignif));
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mul64_Xsig(&accum, &XSIG_LL(argSignif));
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mul64_Xsig(&accum, &XSIG_LL(argSignif));
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mul64_Xsig(&accum, &twothirds);
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shr_Xsig(&accum, -2*(exponent+1));
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/* tan(arg) = arg + accum */
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add_two_Xsig(&accum, &argSignif, &exponent);
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if ( invert )
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{
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/* We now have the value of tan(pi_2 - arg) where pi_2 is an
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approximation for pi/2
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*/
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/* The next step is to fix the answer to compensate for the
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error due to the approximation used for pi/2
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*/
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/* This is (approx) delta, the error in our approx for pi/2
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(see above). It has an exponent of -65
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*/
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XSIG_LL(fix_up) = 0x898cc51701b839a2LL;
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fix_up.lsw = 0;
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if ( exponent == 0 )
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adj = 0xffffffff; /* We want approx 1.0 here, but
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this is close enough. */
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else if ( exponent > -30 )
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{
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adj = accum.msw >> -(exponent+1); /* tan */
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adj = mul_32_32(adj, adj); /* tan^2 */
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}
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else
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adj = 0;
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adj = mul_32_32(0x898cc517, adj); /* delta * tan^2 */
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fix_up.msw += adj;
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if ( !(fix_up.msw & 0x80000000) ) /* did fix_up overflow ? */
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{
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/* Yes, we need to add an msb */
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shr_Xsig(&fix_up, 1);
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fix_up.msw |= 0x80000000;
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shr_Xsig(&fix_up, 64 + exponent);
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}
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else
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shr_Xsig(&fix_up, 65 + exponent);
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add_two_Xsig(&accum, &fix_up, &exponent);
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/* accum now contains tan(pi/2 - arg).
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Use tan(arg) = 1.0 / tan(pi/2 - arg)
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*/
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accumulatoro.lsw = accumulatoro.midw = 0;
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accumulatoro.msw = 0x80000000;
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div_Xsig(&accumulatoro, &accum, &accum);
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exponent = - exponent - 1;
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}
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/* Transfer the result */
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round_Xsig(&accum);
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FPU_settag0(TAG_Valid);
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significand(st0_ptr) = XSIG_LL(accum);
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setexponent16(st0_ptr, exponent + EXTENDED_Ebias); /* Result is positive. */
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}
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