vecemu.c

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/*
 * Routines to emulate some Altivec/VMX instructions, specifically
 * those that can trap when given denormalized operands in Java mode.
 */
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
#include <asm/uaccess.h>

/* Functions in vector.S */
extern void vaddfp(vector128 *dst, vector128 *a, vector128 *b);
extern void vsubfp(vector128 *dst, vector128 *a, vector128 *b);
extern void vmaddfp(vector128 *dst, vector128 *a, vector128 *b, vector128 *c);
extern void vnmsubfp(vector128 *dst, vector128 *a, vector128 *b, vector128 *c);
extern void vrefp(vector128 *dst, vector128 *src);
extern void vrsqrtefp(vector128 *dst, vector128 *src);
extern void vexptep(vector128 *dst, vector128 *src);

static unsigned int exp2s[8] = {
    0x800000,
    0x8b95c2,
    0x9837f0,
    0xa5fed7,
    0xb504f3,
    0xc5672a,
    0xd744fd,
    0xeac0c7
};

/*
 * Computes an estimate of 2^x.  The `s' argument is the 32-bit
 * single-precision floating-point representation of x.
 */
static unsigned int eexp2(unsigned int s)
{
    int exp, pwr;
    unsigned int mant, frac;

    /* extract exponent field from input */
    exp = ((s >> 23) & 0xff) - 127;
    if (exp > 7) {
        /* check for NaN input */
        if (exp == 128 && (s & 0x7fffff) != 0)
            return s | 0x400000;    /* return QNaN */
        /* 2^-big = 0, 2^+big = +Inf */
        return (s & 0x80000000)? 0: 0x7f800000; /* 0 or +Inf */
    }
    if (exp < -23)
        return 0x3f800000;  /* 1.0 */

    /* convert to fixed point integer in 9.23 representation */
    pwr = (s & 0x7fffff) | 0x800000;
    if (exp > 0)
        pwr <<= exp;
    else
        pwr >>= -exp;
    if (s & 0x80000000)
        pwr = -pwr;

    /* extract integer part, which becomes exponent part of result */
    exp = (pwr >> 23) + 126;
    if (exp >= 254)
        return 0x7f800000;
    if (exp < -23)
        return 0;

    /* table lookup on top 3 bits of fraction to get mantissa */
    mant = exp2s[(pwr >> 20) & 7];

    /* linear interpolation using remaining 20 bits of fraction */
    asm("mulhwu %0,%1,%2" : "=r" (frac)
        : "r" (pwr << 12), "r" (0x172b83ff));
    asm("mulhwu %0,%1,%2" : "=r" (frac) : "r" (frac), "r" (mant));
    mant += frac;

    if (exp >= 0)
        return mant + (exp << 23);

    /* denormalized result */
    exp = -exp;
    mant += 1 << (exp - 1);
    return mant >> exp;
}

/*
 * Computes an estimate of log_2(x).  The `s' argument is the 32-bit
 * single-precision floating-point representation of x.
 */
static unsigned int elog2(unsigned int s)
{
    int exp, mant, lz, frac;

    exp = s & 0x7f800000;
    mant = s & 0x7fffff;
    if (exp == 0x7f800000) {    /* Inf or NaN */
        if (mant != 0)
            s |= 0x400000;  /* turn NaN into QNaN */
        return s;
    }
    if ((exp | mant) == 0)      /* +0 or -0 */
        return 0xff800000;  /* return -Inf */

    if (exp == 0) {
        /* denormalized */
        asm("cntlzw %0,%1" : "=r" (lz) : "r" (mant));
        mant <<= lz - 8;
        exp = (-118 - lz) << 23;
    } else {
        mant |= 0x800000;
        exp -= 127 << 23;
    }

    if (mant >= 0xb504f3) {             /* 2^0.5 * 2^23 */
        exp |= 0x400000;            /* 0.5 * 2^23 */
        asm("mulhwu %0,%1,%2" : "=r" (mant)
            : "r" (mant), "r" (0xb504f334));    /* 2^-0.5 * 2^32 */
    }
    if (mant >= 0x9837f0) {             /* 2^0.25 * 2^23 */
        exp |= 0x200000;            /* 0.25 * 2^23 */
        asm("mulhwu %0,%1,%2" : "=r" (mant)
            : "r" (mant), "r" (0xd744fccb));    /* 2^-0.25 * 2^32 */
    }
    if (mant >= 0x8b95c2) {             /* 2^0.125 * 2^23 */
        exp |= 0x100000;            /* 0.125 * 2^23 */
        asm("mulhwu %0,%1,%2" : "=r" (mant)
            : "r" (mant), "r" (0xeac0c6e8));    /* 2^-0.125 * 2^32 */
    }
    if (mant > 0x800000) {              /* 1.0 * 2^23 */
        /* calculate (mant - 1) * 1.381097463 */
        /* 1.381097463 == 0.125 / (2^0.125 - 1) */
        asm("mulhwu %0,%1,%2" : "=r" (frac)
            : "r" ((mant - 0x800000) << 1), "r" (0xb0c7cd3a));
        exp += frac;
    }
    s = exp & 0x80000000;
    if (exp != 0) {
        if (s)
            exp = -exp;
        asm("cntlzw %0,%1" : "=r" (lz) : "r" (exp));
        lz = 8 - lz;
        if (lz > 0)
            exp >>= lz;
        else if (lz < 0)
            exp <<= -lz;
        s += ((lz + 126) << 23) + exp;
    }
    return s;
}

#define VSCR_SAT    1

static int ctsxs(unsigned int x, int scale, unsigned int *vscrp)
{
    int exp, mant;

    exp = (x >> 23) & 0xff;
    mant = x & 0x7fffff;
    if (exp == 255 && mant != 0)
        return 0;       /* NaN -> 0 */
    exp = exp - 127 + scale;
    if (exp < 0)
        return 0;       /* round towards zero */
    if (exp >= 31) {
        /* saturate, unless the result would be -2^31 */
        if (x + (scale << 23) != 0xcf000000)
            *vscrp |= VSCR_SAT;
        return (x & 0x80000000)? 0x80000000: 0x7fffffff;
    }
    mant |= 0x800000;
    mant = (mant << 7) >> (30 - exp);
    return (x & 0x80000000)? -mant: mant;
}

static unsigned int ctuxs(unsigned int x, int scale, unsigned int *vscrp)
{
    int exp;
    unsigned int mant;

    exp = (x >> 23) & 0xff;
    mant = x & 0x7fffff;
    if (exp == 255 && mant != 0)
        return 0;       /* NaN -> 0 */
    exp = exp - 127 + scale;
    if (exp < 0)
        return 0;       /* round towards zero */
    if (x & 0x80000000) {
        /* negative => saturate to 0 */
        *vscrp |= VSCR_SAT;
        return 0;
    }
    if (exp >= 32) {
        /* saturate */
        *vscrp |= VSCR_SAT;
        return 0xffffffff;
    }
    mant |= 0x800000;
    mant = (mant << 8) >> (31 - exp);
    return mant;
}

/* Round to floating integer, towards 0 */
static unsigned int rfiz(unsigned int x)
{
    int exp;

    exp = ((x >> 23) & 0xff) - 127;
    if (exp == 128 && (x & 0x7fffff) != 0)
        return x | 0x400000;    /* NaN -> make it a QNaN */
    if (exp >= 23)
        return x;       /* it's an integer already (or Inf) */
    if (exp < 0)
        return x & 0x80000000;  /* |x| < 1.0 rounds to 0 */
    return x & ~(0x7fffff >> exp);
}

/* Round to floating integer, towards +/- Inf */
static unsigned int rfii(unsigned int x)
{
    int exp, mask;

    exp = ((x >> 23) & 0xff) - 127;
    if (exp == 128 && (x & 0x7fffff) != 0)
        return x | 0x400000;    /* NaN -> make it a QNaN */
    if (exp >= 23)
        return x;       /* it's an integer already (or Inf) */
    if ((x & 0x7fffffff) == 0)
        return x;       /* +/-0 -> +/-0 */
    if (exp < 0)
        /* 0 < |x| < 1.0 rounds to +/- 1.0 */
        return (x & 0x80000000) | 0x3f800000;
    mask = 0x7fffff >> exp;
    /* mantissa overflows into exponent - that's OK,
       it can't overflow into the sign bit */
    return (x + mask) & ~mask;
}

/* Round to floating integer, to nearest */
static unsigned int rfin(unsigned int x)
{
    int exp, half;

    exp = ((x >> 23) & 0xff) - 127;
    if (exp == 128 && (x & 0x7fffff) != 0)
        return x | 0x400000;    /* NaN -> make it a QNaN */
    if (exp >= 23)
        return x;       /* it's an integer already (or Inf) */
    if (exp < -1)
        return x & 0x80000000;  /* |x| < 0.5 -> +/-0 */
    if (exp == -1)
        /* 0.5 <= |x| < 1.0 rounds to +/- 1.0 */
        return (x & 0x80000000) | 0x3f800000;
    half = 0x400000 >> exp;
    /* add 0.5 to the magnitude and chop off the fraction bits */
    return (x + half) & ~(0x7fffff >> exp);
}

int emulate_altivec(struct pt_regs *regs)
{
    unsigned int instr, i;
    unsigned int va, vb, vc, vd;
    vector128 *vrs;

    if (get_user(instr, (unsigned int __user *) regs->nip))
        return -EFAULT;
    if ((instr >> 26) != 4)
        return -EINVAL;     /* not an altivec instruction */
    vd = (instr >> 21) & 0x1f;
    va = (instr >> 16) & 0x1f;
    vb = (instr >> 11) & 0x1f;
    vc = (instr >> 6) & 0x1f;

    vrs = current->thread.vr;
    switch (instr & 0x3f) {
    case 10:
        switch (vc) {
        case 0: /* vaddfp */
            vaddfp(&vrs[vd], &vrs[va], &vrs[vb]);
            break;
        case 1: /* vsubfp */
            vsubfp(&vrs[vd], &vrs[va], &vrs[vb]);
            break;
        case 4: /* vrefp */
            vrefp(&vrs[vd], &vrs[vb]);
            break;
        case 5: /* vrsqrtefp */
            vrsqrtefp(&vrs[vd], &vrs[vb]);
            break;
        case 6: /* vexptefp */
            for (i = 0; i < 4; ++i)
                vrs[vd].u[i] = eexp2(vrs[vb].u[i]);
            break;
        case 7: /* vlogefp */
            for (i = 0; i < 4; ++i)
                vrs[vd].u[i] = elog2(vrs[vb].u[i]);
            break;
        case 8:     /* vrfin */
            for (i = 0; i < 4; ++i)
                vrs[vd].u[i] = rfin(vrs[vb].u[i]);
            break;
        case 9:     /* vrfiz */
            for (i = 0; i < 4; ++i)
                vrs[vd].u[i] = rfiz(vrs[vb].u[i]);
            break;
        case 10:    /* vrfip */
            for (i = 0; i < 4; ++i) {
                u32 x = vrs[vb].u[i];
                x = (x & 0x80000000)? rfiz(x): rfii(x);
                vrs[vd].u[i] = x;
            }
            break;
        case 11:    /* vrfim */
            for (i = 0; i < 4; ++i) {
                u32 x = vrs[vb].u[i];
                x = (x & 0x80000000)? rfii(x): rfiz(x);
                vrs[vd].u[i] = x;
            }
            break;
        case 14:    /* vctuxs */
            for (i = 0; i < 4; ++i)
                vrs[vd].u[i] = ctuxs(vrs[vb].u[i], va,
                        &current->thread.vscr.u[3]);
            break;
        case 15:    /* vctsxs */
            for (i = 0; i < 4; ++i)
                vrs[vd].u[i] = ctsxs(vrs[vb].u[i], va,
                        &current->thread.vscr.u[3]);
            break;
        default:
            return -EINVAL;
        }
        break;
    case 46:    /* vmaddfp */
        vmaddfp(&vrs[vd], &vrs[va], &vrs[vb], &vrs[vc]);
        break;
    case 47:    /* vnmsubfp */
        vnmsubfp(&vrs[vd], &vrs[va], &vrs[vb], &vrs[vc]);
        break;
    default:
        return -EINVAL;
    }

    return 0;
}