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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: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180227143852.11175-27-alex.bennee@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Alex Bennée 2018-03-01 11:05:55 +00:00 committed by Peter Maydell
parent b96a54c7e5
commit d719cbc764
2 changed files with 104 additions and 118 deletions
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221
target/arm/helper.c
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@ -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;
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);
/* 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);
assert(128 <= a && a < 512);
if (a < 256) {
a = a * 2 + 1;
} else {
/* range 0.5 <= a < 1.0 */
/* 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);
/* 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);
a = (a >> 1) << 1;
a = (a + 1) * 2;
}
/* r in units of 1/256 rounded to nearest */
/* s = (int)(256.0 * r + 0.5); */
b = 512;
while (a * (b + 1) * (b + 1) < (1 << 28)) {
b += 1;
}
estimate = (b + 1) / 2;
assert(256 <= estimate && estimate < 512);
q = float64_mul(q, float64_256,s );
q = float64_add(q, float64_half, s);
q_int = float64_to_int64_round_to_zero(q, s);
return estimate;
}
/* return (double)s / 256.0;*/
return float64_div(int64_to_float64(q_int, s), float64_256, 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;
}
if (*exp & 1) {
/* scaled = UInt('01':fraction<51:45>) */
scaled = deposit32(1 << 7, 0, 7, extract64(frac, 45, 7));
} else {
/* scaled = UInt('1':fraction<51:44>) */
scaled = deposit32(1 << 8, 0, 8, extract64(frac, 44, 8));
}
estimate = do_recip_sqrt_estimate(scaled);
*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;
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);
}
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);
f64_frac = recip_sqrt_estimate(&f16_exp, 44, f64_frac);
/* 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);
}
f64_frac = recip_sqrt_estimate(&f32_exp, 380, f64_frac);
result_exp = (380 - f32_exp) / 2;
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. */
f64_frac = recip_sqrt_estimate(&f64_exp, 3068, f64_frac);
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;
}
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));
}
estimate = do_recip_sqrt_estimate(extract32(a, 23, 9));
f64 = recip_sqrt_estimate(f64, fpst);
return 0x80000000 | ((float64_val(f64) >> 21) & 0x7fffffff);
return deposit32(0, 23, 9, estimate);
}
/* VFPv4 fused multiply-accumulate */

1
target/arm/helper.h
View File

@ -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)