cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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poly_2xm1.c (4512B)

      1// SPDX-License-Identifier: GPL-2.0
      2/*---------------------------------------------------------------------------+
      3 |  poly_2xm1.c                                                              |
      4 |                                                                           |
      5 | Function to compute 2^x-1 by a polynomial approximation.                  |
      6 |                                                                           |
      7 | Copyright (C) 1992,1993,1994,1997                                         |
      8 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
      9 |                  E-mail   billm@suburbia.net                              |
     10 |                                                                           |
     11 |                                                                           |
     12 +---------------------------------------------------------------------------*/
     13
     14#include "exception.h"
     15#include "reg_constant.h"
     16#include "fpu_emu.h"
     17#include "fpu_system.h"
     18#include "control_w.h"
     19#include "poly.h"
     20
     21#define	HIPOWER	11
     22static const unsigned long long lterms[HIPOWER] = {
     23	0x0000000000000000LL,	/* This term done separately as 12 bytes */
     24	0xf5fdeffc162c7543LL,
     25	0x1c6b08d704a0bfa6LL,
     26	0x0276556df749cc21LL,
     27	0x002bb0ffcf14f6b8LL,
     28	0x0002861225ef751cLL,
     29	0x00001ffcbfcd5422LL,
     30	0x00000162c005d5f1LL,
     31	0x0000000da96ccb1bLL,
     32	0x0000000078d1b897LL,
     33	0x000000000422b029LL
     34};
     35
     36static const Xsig hiterm = MK_XSIG(0xb17217f7, 0xd1cf79ab, 0xc8a39194);
     37
     38/* Four slices: 0.0 : 0.25 : 0.50 : 0.75 : 1.0,
     39   These numbers are 2^(1/4), 2^(1/2), and 2^(3/4)
     40 */
     41static const Xsig shiftterm0 = MK_XSIG(0, 0, 0);
     42static const Xsig shiftterm1 = MK_XSIG(0x9837f051, 0x8db8a96f, 0x46ad2318);
     43static const Xsig shiftterm2 = MK_XSIG(0xb504f333, 0xf9de6484, 0x597d89b3);
     44static const Xsig shiftterm3 = MK_XSIG(0xd744fcca, 0xd69d6af4, 0x39a68bb9);
     45
     46static const Xsig *shiftterm[] = { &shiftterm0, &shiftterm1,
     47	&shiftterm2, &shiftterm3
     48};
     49
     50/*--- poly_2xm1() -----------------------------------------------------------+
     51 | Requires st(0) which is TAG_Valid and < 1.                                |
     52 +---------------------------------------------------------------------------*/
     53int poly_2xm1(u_char sign, FPU_REG *arg, FPU_REG *result)
     54{
     55	long int exponent, shift;
     56	unsigned long long Xll;
     57	Xsig accumulator, Denom, argSignif;
     58	u_char tag;
     59
     60	exponent = exponent16(arg);
     61
     62#ifdef PARANOID
     63	if (exponent >= 0) {	/* Don't want a |number| >= 1.0 */
     64		/* Number negative, too large, or not Valid. */
     65		EXCEPTION(EX_INTERNAL | 0x127);
     66		return 1;
     67	}
     68#endif /* PARANOID */
     69
     70	argSignif.lsw = 0;
     71	XSIG_LL(argSignif) = Xll = significand(arg);
     72
     73	if (exponent == -1) {
     74		shift = (argSignif.msw & 0x40000000) ? 3 : 2;
     75		/* subtract 0.5 or 0.75 */
     76		exponent -= 2;
     77		XSIG_LL(argSignif) <<= 2;
     78		Xll <<= 2;
     79	} else if (exponent == -2) {
     80		shift = 1;
     81		/* subtract 0.25 */
     82		exponent--;
     83		XSIG_LL(argSignif) <<= 1;
     84		Xll <<= 1;
     85	} else
     86		shift = 0;
     87
     88	if (exponent < -2) {
     89		/* Shift the argument right by the required places. */
     90		if (FPU_shrx(&Xll, -2 - exponent) >= 0x80000000U)
     91			Xll++;	/* round up */
     92	}
     93
     94	accumulator.lsw = accumulator.midw = accumulator.msw = 0;
     95	polynomial_Xsig(&accumulator, &Xll, lterms, HIPOWER - 1);
     96	mul_Xsig_Xsig(&accumulator, &argSignif);
     97	shr_Xsig(&accumulator, 3);
     98
     99	mul_Xsig_Xsig(&argSignif, &hiterm);	/* The leading term */
    100	add_two_Xsig(&accumulator, &argSignif, &exponent);
    101
    102	if (shift) {
    103		/* The argument is large, use the identity:
    104		   f(x+a) = f(a) * (f(x) + 1) - 1;
    105		 */
    106		shr_Xsig(&accumulator, -exponent);
    107		accumulator.msw |= 0x80000000;	/* add 1.0 */
    108		mul_Xsig_Xsig(&accumulator, shiftterm[shift]);
    109		accumulator.msw &= 0x3fffffff;	/* subtract 1.0 */
    110		exponent = 1;
    111	}
    112
    113	if (sign != SIGN_POS) {
    114		/* The argument is negative, use the identity:
    115		   f(-x) = -f(x) / (1 + f(x))
    116		 */
    117		Denom.lsw = accumulator.lsw;
    118		XSIG_LL(Denom) = XSIG_LL(accumulator);
    119		if (exponent < 0)
    120			shr_Xsig(&Denom, -exponent);
    121		else if (exponent > 0) {
    122			/* exponent must be 1 here */
    123			XSIG_LL(Denom) <<= 1;
    124			if (Denom.lsw & 0x80000000)
    125				XSIG_LL(Denom) |= 1;
    126			(Denom.lsw) <<= 1;
    127		}
    128		Denom.msw |= 0x80000000;	/* add 1.0 */
    129		div_Xsig(&accumulator, &Denom, &accumulator);
    130	}
    131
    132	/* Convert to 64 bit signed-compatible */
    133	exponent += round_Xsig(&accumulator);
    134
    135	result = &st(0);
    136	significand(result) = XSIG_LL(accumulator);
    137	setexponent16(result, exponent);
    138
    139	tag = FPU_round(result, 1, 0, FULL_PRECISION, sign);
    140
    141	setsign(result, sign);
    142	FPU_settag0(tag);
    143
    144	return 0;
    145
    146}