Commit d719cbc7 authored by Alex Bennée's avatar Alex Bennée Committed by Peter Maydell
Browse files

arm/helper.c: re-factor rsqrte and add rsqrte_f16 



Much like recpe the ARM ARM has simplified the pseudo code for the
calculation which is done on a fixed point 9 bit integer maths. So
while adding f16 we can also clean this up to be a little less heavy
on the floating point and just return the fractional part and leave
the calle's to do the final packing of the result.

Signed-off-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: default avatarRichard Henderson <richard.henderson@linaro.org>
Message-id: 20180227143852.11175-27-alex.bennee@linaro.org
Signed-off-by: default avatarPeter Maydell <peter.maydell@linaro.org>
parent b96a54c7

target/arm/helper.c

+103 −118
Original line number Diff line number Diff line
@@ -11756,56 +11756,97 @@ float64 HELPER(recpe_f64)(float64 input, void *fpstp) 
/* The algorithm that must be used to calculate the estimate

 * is specified by the ARM ARM.

 */

static float64 recip_sqrt_estimate(float64 a, float_status *real_fp_status)



static int do_recip_sqrt_estimate(int a)

{

    /* These calculations mustn't set any fp exception flags,

     * so we use a local copy of the fp_status.

     */

    float_status dummy_status = *real_fp_status;

    float_status *s = &dummy_status;

    float64 q;

    int64_t q_int;

    int b, estimate;



    assert(128 <= a && a < 512);

    if (a < 256) {

        a = a * 2 + 1;

    } else {

        a = (a >> 1) << 1;

        a = (a + 1) * 2;

    }

    b = 512;

    while (a * (b + 1) * (b + 1) < (1 << 28)) {

        b += 1;

    }

    estimate = (b + 1) / 2;

    assert(256 <= estimate && estimate < 512);



    return estimate;

}



    if (float64_lt(a, float64_half, s)) {

        /* range 0.25 <= a < 0.5 */



        /* a in units of 1/512 rounded down */

        /* q0 = (int)(a * 512.0);  */

        q = float64_mul(float64_512, a, s);

        q_int = float64_to_int64_round_to_zero(q, s);

static uint64_t recip_sqrt_estimate(int *exp , int exp_off, uint64_t frac)

{

    int estimate;

    uint32_t scaled;



    if (*exp == 0) {

        while (extract64(frac, 51, 1) == 0) {

            frac = frac << 1;

            *exp -= 1;

        }

        frac = extract64(frac, 0, 51) << 1;

    }



        /* reciprocal root r */

        /* r = 1.0 / sqrt(((double)q0 + 0.5) / 512.0);  */

        q = int64_to_float64(q_int, s);

        q = float64_add(q, float64_half, s);

        q = float64_div(q, float64_512, s);

        q = float64_sqrt(q, s);

        q = float64_div(float64_one, q, s);

    if (*exp & 1) {

        /* scaled = UInt('01':fraction<51:45>) */

        scaled = deposit32(1 << 7, 0, 7, extract64(frac, 45, 7));

    } else {

        /* range 0.5 <= a < 1.0 */

        /* scaled = UInt('1':fraction<51:44>) */

        scaled = deposit32(1 << 8, 0, 8, extract64(frac, 44, 8));

    }

    estimate = do_recip_sqrt_estimate(scaled);



        /* a in units of 1/256 rounded down */

        /* q1 = (int)(a * 256.0); */

        q = float64_mul(float64_256, a, s);

        int64_t q_int = float64_to_int64_round_to_zero(q, s);

    *exp = (exp_off - *exp) / 2;

    return extract64(estimate, 0, 8) << 44;

}



float16 HELPER(rsqrte_f16)(float16 input, void *fpstp)

{

    float_status *s = fpstp;

    float16 f16 = float16_squash_input_denormal(input, s);

    uint16_t val = float16_val(f16);

    bool f16_sign = float16_is_neg(f16);

    int f16_exp = extract32(val, 10, 5);

    uint16_t f16_frac = extract32(val, 0, 10);

    uint64_t f64_frac;



        /* reciprocal root r */

        /* r = 1.0 /sqrt(((double)q1 + 0.5) / 256); */

        q = int64_to_float64(q_int, s);

        q = float64_add(q, float64_half, s);

        q = float64_div(q, float64_256, s);

        q = float64_sqrt(q, s);

        q = float64_div(float64_one, q, s);

    if (float16_is_any_nan(f16)) {

        float16 nan = f16;

        if (float16_is_signaling_nan(f16, s)) {

            float_raise(float_flag_invalid, s);

            nan = float16_maybe_silence_nan(f16, s);

        }

    /* r in units of 1/256 rounded to nearest */

    /* s = (int)(256.0 * r + 0.5); */

        if (s->default_nan_mode) {

            nan =  float16_default_nan(s);

        }

        return nan;

    } else if (float16_is_zero(f16)) {

        float_raise(float_flag_divbyzero, s);

        return float16_set_sign(float16_infinity, f16_sign);

    } else if (f16_sign) {

        float_raise(float_flag_invalid, s);

        return float16_default_nan(s);

    } else if (float16_is_infinity(f16)) {

        return float16_zero;

    }



    /* Scale and normalize to a double-precision value between 0.25 and 1.0,

     * preserving the parity of the exponent.  */



    f64_frac = ((uint64_t) f16_frac) << (52 - 10);



    q = float64_mul(q, float64_256,s );

    q = float64_add(q, float64_half, s);

    q_int = float64_to_int64_round_to_zero(q, s);

    f64_frac = recip_sqrt_estimate(&f16_exp, 44, f64_frac);



    /* return (double)s / 256.0;*/

    return float64_div(int64_to_float64(q_int, s), float64_256, s);

    /* result = sign : result_exp<4:0> : estimate<7:0> : Zeros(2) */

    val = deposit32(0, 15, 1, f16_sign);

    val = deposit32(val, 10, 5, f16_exp);

    val = deposit32(val, 2, 8, extract64(f64_frac, 52 - 8, 8));

    return make_float16(val);

}



float32 HELPER(rsqrte_f32)(float32 input, void *fpstp)
@@ -11813,13 +11854,10 @@ float32 HELPER(rsqrte_f32)(float32 input, void *fpstp) 
    float_status *s = fpstp;

    float32 f32 = float32_squash_input_denormal(input, s);

    uint32_t val = float32_val(f32);

    uint32_t f32_sbit = 0x80000000 & val;

    int32_t f32_exp = extract32(val, 23, 8);

    uint32_t f32_sign = float32_is_neg(f32);

    int f32_exp = extract32(val, 23, 8);

    uint32_t f32_frac = extract32(val, 0, 23);

    uint64_t f64_frac;

    uint64_t val64;

    int result_exp;

    float64 f64;



    if (float32_is_any_nan(f32)) {

        float32 nan = f32;
@@ -11845,32 +11883,13 @@ float32 HELPER(rsqrte_f32)(float32 input, void *fpstp) 
     * preserving the parity of the exponent.  */



    f64_frac = ((uint64_t) f32_frac) << 29;

    if (f32_exp == 0) {

        while (extract64(f64_frac, 51, 1) == 0) {

            f64_frac = f64_frac << 1;

            f32_exp = f32_exp-1;

        }

        f64_frac = extract64(f64_frac, 0, 51) << 1;

    }



    if (extract64(f32_exp, 0, 1) == 0) {

        f64 = make_float64(((uint64_t) f32_sbit) << 32

                           | (0x3feULL << 52)

                           | f64_frac);

    } else {

        f64 = make_float64(((uint64_t) f32_sbit) << 32

                           | (0x3fdULL << 52)

                           | f64_frac);

    }



    result_exp = (380 - f32_exp) / 2;

    f64_frac = recip_sqrt_estimate(&f32_exp, 380, f64_frac);



    f64 = recip_sqrt_estimate(f64, s);



    val64 = float64_val(f64);



    val = ((result_exp & 0xff) << 23)

        | ((val64 >> 29)  & 0x7fffff);

    /* result = sign : result_exp<4:0> : estimate<7:0> : Zeros(15) */

    val = deposit32(0, 31, 1, f32_sign);

    val = deposit32(val, 23, 8, f32_exp);

    val = deposit32(val, 15, 8, extract64(f64_frac, 52 - 8, 8));

    return make_float32(val);

}
@@ -11879,11 +11898,9 @@ float64 HELPER(rsqrte_f64)(float64 input, void *fpstp) 
    float_status *s = fpstp;

    float64 f64 = float64_squash_input_denormal(input, s);

    uint64_t val = float64_val(f64);

    uint64_t f64_sbit = 0x8000000000000000ULL & val;

    int64_t f64_exp = extract64(val, 52, 11);

    bool f64_sign = float64_is_neg(f64);

    int f64_exp = extract64(val, 52, 11);

    uint64_t f64_frac = extract64(val, 0, 52);

    int64_t result_exp;

    uint64_t result_frac;



    if (float64_is_any_nan(f64)) {

        float64 nan = f64;
@@ -11905,36 +11922,13 @@ float64 HELPER(rsqrte_f64)(float64 input, void *fpstp) 
        return float64_zero;

    }



    /* Scale and normalize to a double-precision value between 0.25 and 1.0,

     * preserving the parity of the exponent.  */



    if (f64_exp == 0) {

        while (extract64(f64_frac, 51, 1) == 0) {

            f64_frac = f64_frac << 1;

            f64_exp = f64_exp - 1;

        }

        f64_frac = extract64(f64_frac, 0, 51) << 1;

    }

    f64_frac = recip_sqrt_estimate(&f64_exp, 3068, f64_frac);



    if (extract64(f64_exp, 0, 1) == 0) {

        f64 = make_float64(f64_sbit

                           | (0x3feULL << 52)

                           | f64_frac);

    } else {

        f64 = make_float64(f64_sbit

                           | (0x3fdULL << 52)

                           | f64_frac);

    }



    result_exp = (3068 - f64_exp) / 2;



    f64 = recip_sqrt_estimate(f64, s);



    result_frac = extract64(float64_val(f64), 0, 52);



    return make_float64(f64_sbit |

                        ((result_exp & 0x7ff) << 52) |

                        result_frac);

    /* result = sign : result_exp<4:0> : estimate<7:0> : Zeros(44) */

    val = deposit64(0, 61, 1, f64_sign);

    val = deposit64(val, 52, 11, f64_exp);

    val = deposit64(val, 44, 8, extract64(f64_frac, 52 - 8, 8));

    return make_float64(val);

}



uint32_t HELPER(recpe_u32)(uint32_t a, void *fpstp)
@@ -11954,24 +11948,15 @@ uint32_t HELPER(recpe_u32)(uint32_t a, void *fpstp) 


uint32_t HELPER(rsqrte_u32)(uint32_t a, void *fpstp)

{

    float_status *fpst = fpstp;

    float64 f64;

    int estimate;



    if ((a & 0xc0000000) == 0) {

        return 0xffffffff;

    }



    if (a & 0x80000000) {

        f64 = make_float64((0x3feULL << 52)

                           | ((uint64_t)(a & 0x7fffffff) << 21));

    } else { /* bits 31-30 == '01' */

        f64 = make_float64((0x3fdULL << 52)

                           | ((uint64_t)(a & 0x3fffffff) << 22));

    }



    f64 = recip_sqrt_estimate(f64, fpst);

    estimate = do_recip_sqrt_estimate(extract32(a, 23, 9));



    return 0x80000000 | ((float64_val(f64) >> 21) & 0x7fffffff);

    return deposit32(0, 23, 9, estimate);

}



/* VFPv4 fused multiply-accumulate */

target/arm/helper.h

+1 −0
Original line number Diff line number Diff line
@@ -195,6 +195,7 @@ DEF_HELPER_3(rsqrts_f32, f32, f32, f32, env) 
DEF_HELPER_FLAGS_2(recpe_f16, TCG_CALL_NO_RWG, f16, f16, ptr)

DEF_HELPER_FLAGS_2(recpe_f32, TCG_CALL_NO_RWG, f32, f32, ptr)

DEF_HELPER_FLAGS_2(recpe_f64, TCG_CALL_NO_RWG, f64, f64, ptr)

DEF_HELPER_FLAGS_2(rsqrte_f16, TCG_CALL_NO_RWG, f16, f16, ptr)

DEF_HELPER_FLAGS_2(rsqrte_f32, TCG_CALL_NO_RWG, f32, f32, ptr)

DEF_HELPER_FLAGS_2(rsqrte_f64, TCG_CALL_NO_RWG, f64, f64, ptr)

DEF_HELPER_2(recpe_u32, i32, i32, ptr)