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-rw-r--r--arch/x86/math-emu/poly_l2.c245
1 files changed, 245 insertions, 0 deletions
diff --git a/arch/x86/math-emu/poly_l2.c b/arch/x86/math-emu/poly_l2.c
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index 000000000..98b6949bb
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+++ b/arch/x86/math-emu/poly_l2.c
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+// SPDX-License-Identifier: GPL-2.0
+/*---------------------------------------------------------------------------+
+ | 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;
+
+}
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