+++ /dev/null
-/*---------------------------------------------------------------------------+
- | poly_l2.c |
- | |
- | Compute the base 2 log of a FPU_REG, using a polynomial approximation. |
- | |
- | Copyright (C) 1992,1993,1994,1997 |
- | W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
- | E-mail billm@suburbia.net |
- | |
- | |
- +---------------------------------------------------------------------------*/
-
-
-#include "exception.h"
-#include "reg_constant.h"
-#include "fpu_emu.h"
-#include "fpu_system.h"
-#include "control_w.h"
-#include "poly.h"
-
-
-static void log2_kernel(FPU_REG const *arg, u_char argsign,
- Xsig *accum_result, long int *expon);
-
-
-/*--- poly_l2() -------------------------------------------------------------+
- | Base 2 logarithm by a polynomial approximation. |
- +---------------------------------------------------------------------------*/
-void poly_l2(FPU_REG *st0_ptr, FPU_REG *st1_ptr, u_char st1_sign)
-{
- long int exponent, expon, expon_expon;
- Xsig accumulator, expon_accum, yaccum;
- u_char sign, argsign;
- FPU_REG x;
- int tag;
-
- exponent = exponent16(st0_ptr);
-
- /* From st0_ptr, make a number > sqrt(2)/2 and < sqrt(2) */
- if ( st0_ptr->sigh > (unsigned)0xb504f334 )
- {
- /* Treat as sqrt(2)/2 < st0_ptr < 1 */
- significand(&x) = - significand(st0_ptr);
- setexponent16(&x, -1);
- exponent++;
- argsign = SIGN_NEG;
- }
- else
- {
- /* Treat as 1 <= st0_ptr < sqrt(2) */
- x.sigh = st0_ptr->sigh - 0x80000000;
- x.sigl = st0_ptr->sigl;
- setexponent16(&x, 0);
- argsign = SIGN_POS;
- }
- tag = FPU_normalize_nuo(&x);
-
- if ( tag == TAG_Zero )
- {
- expon = 0;
- accumulator.msw = accumulator.midw = accumulator.lsw = 0;
- }
- else
- {
- log2_kernel(&x, argsign, &accumulator, &expon);
- }
-
- if ( exponent < 0 )
- {
- sign = SIGN_NEG;
- exponent = -exponent;
- }
- else
- sign = SIGN_POS;
- expon_accum.msw = exponent; expon_accum.midw = expon_accum.lsw = 0;
- if ( exponent )
- {
- expon_expon = 31 + norm_Xsig(&expon_accum);
- shr_Xsig(&accumulator, expon_expon - expon);
-
- if ( sign ^ argsign )
- negate_Xsig(&accumulator);
- add_Xsig_Xsig(&accumulator, &expon_accum);
- }
- else
- {
- expon_expon = expon;
- sign = argsign;
- }
-
- yaccum.lsw = 0; XSIG_LL(yaccum) = significand(st1_ptr);
- mul_Xsig_Xsig(&accumulator, &yaccum);
-
- expon_expon += round_Xsig(&accumulator);
-
- if ( accumulator.msw == 0 )
- {
- FPU_copy_to_reg1(&CONST_Z, TAG_Zero);
- return;
- }
-
- significand(st1_ptr) = XSIG_LL(accumulator);
- setexponent16(st1_ptr, expon_expon + exponent16(st1_ptr) + 1);
-
- tag = FPU_round(st1_ptr, 1, 0, FULL_PRECISION, sign ^ st1_sign);
- FPU_settagi(1, tag);
-
- set_precision_flag_up(); /* 80486 appears to always do this */
-
- return;
-
-}
-
-
-/*--- poly_l2p1() -----------------------------------------------------------+
- | Base 2 logarithm by a polynomial approximation. |
- | log2(x+1) |
- +---------------------------------------------------------------------------*/
-int poly_l2p1(u_char sign0, u_char sign1,
- FPU_REG *st0_ptr, FPU_REG *st1_ptr, FPU_REG *dest)
-{
- u_char tag;
- long int exponent;
- Xsig accumulator, yaccum;
-
- if ( exponent16(st0_ptr) < 0 )
- {
- log2_kernel(st0_ptr, sign0, &accumulator, &exponent);
-
- yaccum.lsw = 0;
- XSIG_LL(yaccum) = significand(st1_ptr);
- mul_Xsig_Xsig(&accumulator, &yaccum);
-
- exponent += round_Xsig(&accumulator);
-
- exponent += exponent16(st1_ptr) + 1;
- if ( exponent < EXP_WAY_UNDER ) exponent = EXP_WAY_UNDER;
-
- significand(dest) = XSIG_LL(accumulator);
- setexponent16(dest, exponent);
-
- tag = FPU_round(dest, 1, 0, FULL_PRECISION, sign0 ^ sign1);
- FPU_settagi(1, tag);
-
- if ( tag == TAG_Valid )
- set_precision_flag_up(); /* 80486 appears to always do this */
- }
- else
- {
- /* The magnitude of st0_ptr is far too large. */
-
- if ( sign0 != SIGN_POS )
- {
- /* Trying to get the log of a negative number. */
-#ifdef PECULIAR_486 /* Stupid 80486 doesn't worry about log(negative). */
- changesign(st1_ptr);
-#else
- if ( arith_invalid(1) < 0 )
- return 1;
-#endif /* PECULIAR_486 */
- }
-
- /* 80486 appears to do this */
- if ( sign0 == SIGN_NEG )
- set_precision_flag_down();
- else
- set_precision_flag_up();
- }
-
- if ( exponent(dest) <= EXP_UNDER )
- EXCEPTION(EX_Underflow);
-
- return 0;
-
-}
-
-
-
-
-#undef HIPOWER
-#define HIPOWER 10
-static const unsigned long long logterms[HIPOWER] =
-{
- 0x2a8eca5705fc2ef0LL,
- 0xf6384ee1d01febceLL,
- 0x093bb62877cdf642LL,
- 0x006985d8a9ec439bLL,
- 0x0005212c4f55a9c8LL,
- 0x00004326a16927f0LL,
- 0x0000038d1d80a0e7LL,
- 0x0000003141cc80c6LL,
- 0x00000002b1668c9fLL,
- 0x000000002c7a46aaLL
-};
-
-static const unsigned long leadterm = 0xb8000000;
-
-
-/*--- log2_kernel() ---------------------------------------------------------+
- | Base 2 logarithm by a polynomial approximation. |
- | log2(x+1) |
- +---------------------------------------------------------------------------*/
-static void log2_kernel(FPU_REG const *arg, u_char argsign, Xsig *accum_result,
- long int *expon)
-{
- long int exponent, adj;
- unsigned long long Xsq;
- Xsig accumulator, Numer, Denom, argSignif, arg_signif;
-
- exponent = exponent16(arg);
- Numer.lsw = Denom.lsw = 0;
- XSIG_LL(Numer) = XSIG_LL(Denom) = significand(arg);
- if ( argsign == SIGN_POS )
- {
- shr_Xsig(&Denom, 2 - (1 + exponent));
- Denom.msw |= 0x80000000;
- div_Xsig(&Numer, &Denom, &argSignif);
- }
- else
- {
- shr_Xsig(&Denom, 1 - (1 + exponent));
- negate_Xsig(&Denom);
- if ( Denom.msw & 0x80000000 )
- {
- div_Xsig(&Numer, &Denom, &argSignif);
- exponent ++;
- }
- else
- {
- /* Denom must be 1.0 */
- argSignif.lsw = Numer.lsw; argSignif.midw = Numer.midw;
- argSignif.msw = Numer.msw;
- }
- }
-
-#ifndef PECULIAR_486
- /* Should check here that |local_arg| is within the valid range */
- if ( exponent >= -2 )
- {
- if ( (exponent > -2) ||
- (argSignif.msw > (unsigned)0xafb0ccc0) )
- {
- /* The argument is too large */
- }
- }
-#endif /* PECULIAR_486 */
-
- arg_signif.lsw = argSignif.lsw; XSIG_LL(arg_signif) = XSIG_LL(argSignif);
- adj = norm_Xsig(&argSignif);
- accumulator.lsw = argSignif.lsw; XSIG_LL(accumulator) = XSIG_LL(argSignif);
- mul_Xsig_Xsig(&accumulator, &accumulator);
- shr_Xsig(&accumulator, 2*(-1 - (1 + exponent + adj)));
- Xsq = XSIG_LL(accumulator);
- if ( accumulator.lsw & 0x80000000 )
- Xsq++;
-
- accumulator.msw = accumulator.midw = accumulator.lsw = 0;
- /* Do the basic fixed point polynomial evaluation */
- polynomial_Xsig(&accumulator, &Xsq, logterms, HIPOWER-1);
-
- mul_Xsig_Xsig(&accumulator, &argSignif);
- shr_Xsig(&accumulator, 6 - adj);
-
- mul32_Xsig(&arg_signif, leadterm);
- add_two_Xsig(&accumulator, &arg_signif, &exponent);
-
- *expon = exponent + 1;
- accum_result->lsw = accumulator.lsw;
- accum_result->midw = accumulator.midw;
- accum_result->msw = accumulator.msw;
-
-}
git.openpandora.org / pandora-kernel.git / blobdiff