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authorAlex Bennée <alex.bennee@linaro.org>2018-03-01 11:05:54 +0000
committerPeter Maydell <peter.maydell@linaro.org>2018-03-01 11:13:59 +0000
commit5eb70735af1c0b607bf2671a53aff3710cc1672f (patch)
tree4e49acfabfc565719f5470dc1141c25bd0187e8c /target/arm/helper.c
parent15f8a233c8c023dbc77b6fe6cd7c79eac9bee263 (diff)
arm/helper.c: re-factor recpe and add recepe_f16
It looks like 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: 20180227143852.11175-23-alex.bennee@linaro.org Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Diffstat (limited to 'target/arm/helper.c')
-rw-r--r--target/arm/helper.c224
1 files changed, 127 insertions, 97 deletions
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 6e3dadb754..e2d0ff0b4c 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -11523,80 +11523,75 @@ float32 HELPER(rsqrts_f32)(float32 a, float32 b, CPUARMState *env)
* int->float conversions at run-time. */
#define float64_256 make_float64(0x4070000000000000LL)
#define float64_512 make_float64(0x4080000000000000LL)
+#define float16_maxnorm make_float16(0x7bff)
#define float32_maxnorm make_float32(0x7f7fffff)
#define float64_maxnorm make_float64(0x7fefffffffffffffLL)
/* Reciprocal functions
*
* The algorithm that must be used to calculate the estimate
- * is specified by the ARM ARM, see FPRecipEstimate()
+ * is specified by the ARM ARM, see FPRecipEstimate()/RecipEstimate
*/
-static float64 recip_estimate(float64 a, float_status *real_fp_status)
-{
- /* 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;
- /* q = (int)(a * 512.0) */
- float64 q = float64_mul(float64_512, a, s);
- int64_t q_int = float64_to_int64_round_to_zero(q, s);
-
- /* r = 1.0 / (((double)q + 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_div(float64_one, q, s);
-
- /* s = (int)(256.0 * r + 0.5) */
- q = float64_mul(q, float64_256, s);
- q = float64_add(q, float64_half, s);
- q_int = float64_to_int64_round_to_zero(q, s);
+/* See RecipEstimate()
+ *
+ * input is a 9 bit fixed point number
+ * input range 256 .. 511 for a number from 0.5 <= x < 1.0.
+ * result range 256 .. 511 for a number from 1.0 to 511/256.
+ */
- /* return (double)s / 256.0 */
- return float64_div(int64_to_float64(q_int, s), float64_256, s);
+static int recip_estimate(int input)
+{
+ int a, b, r;
+ assert(256 <= input && input < 512);
+ a = (input * 2) + 1;
+ b = (1 << 19) / a;
+ r = (b + 1) >> 1;
+ assert(256 <= r && r < 512);
+ return r;
}
-/* Common wrapper to call recip_estimate */
-static float64 call_recip_estimate(float64 num, int off, float_status *fpst)
+/*
+ * Common wrapper to call recip_estimate
+ *
+ * The parameters are exponent and 64 bit fraction (without implicit
+ * bit) where the binary point is nominally at bit 52. Returns a
+ * float64 which can then be rounded to the appropriate size by the
+ * callee.
+ */
+
+static uint64_t call_recip_estimate(int *exp, int exp_off, uint64_t frac)
{
- uint64_t val64 = float64_val(num);
- uint64_t frac = extract64(val64, 0, 52);
- int64_t exp = extract64(val64, 52, 11);
- uint64_t sbit;
- float64 scaled, estimate;
+ uint32_t scaled, estimate;
+ uint64_t result_frac;
+ int result_exp;
- /* Generate the scaled number for the estimate function */
- if (exp == 0) {
+ /* Handle sub-normals */
+ if (*exp == 0) {
if (extract64(frac, 51, 1) == 0) {
- exp = -1;
- frac = extract64(frac, 0, 50) << 2;
+ *exp = -1;
+ frac <<= 2;
} else {
- frac = extract64(frac, 0, 51) << 1;
+ frac <<= 1;
}
}
- /* scaled = '0' : '01111111110' : fraction<51:44> : Zeros(44); */
- scaled = make_float64((0x3feULL << 52)
- | extract64(frac, 44, 8) << 44);
-
- estimate = recip_estimate(scaled, fpst);
+ /* scaled = UInt('1':fraction<51:44>) */
+ scaled = deposit32(1 << 8, 0, 8, extract64(frac, 44, 8));
+ estimate = recip_estimate(scaled);
- /* Build new result */
- val64 = float64_val(estimate);
- sbit = 0x8000000000000000ULL & val64;
- exp = off - exp;
- frac = extract64(val64, 0, 52);
-
- if (exp == 0) {
- frac = 1ULL << 51 | extract64(frac, 1, 51);
- } else if (exp == -1) {
- frac = 1ULL << 50 | extract64(frac, 2, 50);
- exp = 0;
+ result_exp = exp_off - *exp;
+ result_frac = deposit64(0, 44, 8, estimate);
+ if (result_exp == 0) {
+ result_frac = deposit64(result_frac >> 1, 51, 1, 1);
+ } else if (result_exp == -1) {
+ result_frac = deposit64(result_frac >> 2, 50, 2, 1);
+ result_exp = 0;
}
- return make_float64(sbit | (exp << 52) | frac);
+ *exp = result_exp;
+
+ return result_frac;
}
static bool round_to_inf(float_status *fpst, bool sign_bit)
@@ -11615,18 +11610,63 @@ static bool round_to_inf(float_status *fpst, bool sign_bit)
g_assert_not_reached();
}
+float16 HELPER(recpe_f16)(float16 input, void *fpstp)
+{
+ float_status *fpst = fpstp;
+ float16 f16 = float16_squash_input_denormal(input, fpst);
+ uint32_t f16_val = float16_val(f16);
+ uint32_t f16_sign = float16_is_neg(f16);
+ int f16_exp = extract32(f16_val, 10, 5);
+ uint32_t f16_frac = extract32(f16_val, 0, 10);
+ uint64_t f64_frac;
+
+ if (float16_is_any_nan(f16)) {
+ float16 nan = f16;
+ if (float16_is_signaling_nan(f16, fpst)) {
+ float_raise(float_flag_invalid, fpst);
+ nan = float16_maybe_silence_nan(f16, fpst);
+ }
+ if (fpst->default_nan_mode) {
+ nan = float16_default_nan(fpst);
+ }
+ return nan;
+ } else if (float16_is_infinity(f16)) {
+ return float16_set_sign(float16_zero, float16_is_neg(f16));
+ } else if (float16_is_zero(f16)) {
+ float_raise(float_flag_divbyzero, fpst);
+ return float16_set_sign(float16_infinity, float16_is_neg(f16));
+ } else if (float16_abs(f16) < (1 << 8)) {
+ /* Abs(value) < 2.0^-16 */
+ float_raise(float_flag_overflow | float_flag_inexact, fpst);
+ if (round_to_inf(fpst, f16_sign)) {
+ return float16_set_sign(float16_infinity, f16_sign);
+ } else {
+ return float16_set_sign(float16_maxnorm, f16_sign);
+ }
+ } else if (f16_exp >= 29 && fpst->flush_to_zero) {
+ float_raise(float_flag_underflow, fpst);
+ return float16_set_sign(float16_zero, float16_is_neg(f16));
+ }
+
+ f64_frac = call_recip_estimate(&f16_exp, 29,
+ ((uint64_t) f16_frac) << (52 - 10));
+
+ /* result = sign : result_exp<4:0> : fraction<51:42> */
+ f16_val = deposit32(0, 15, 1, f16_sign);
+ f16_val = deposit32(f16_val, 10, 5, f16_exp);
+ f16_val = deposit32(f16_val, 0, 10, extract64(f64_frac, 52 - 10, 10));
+ return make_float16(f16_val);
+}
+
float32 HELPER(recpe_f32)(float32 input, void *fpstp)
{
float_status *fpst = fpstp;
float32 f32 = float32_squash_input_denormal(input, fpst);
uint32_t f32_val = float32_val(f32);
- uint32_t f32_sbit = 0x80000000ULL & f32_val;
- int32_t f32_exp = extract32(f32_val, 23, 8);
+ bool f32_sign = float32_is_neg(f32);
+ int f32_exp = extract32(f32_val, 23, 8);
uint32_t f32_frac = extract32(f32_val, 0, 23);
- float64 f64, r64;
- uint64_t r64_val;
- int64_t r64_exp;
- uint64_t r64_frac;
+ uint64_t f64_frac;
if (float32_is_any_nan(f32)) {
float32 nan = f32;
@@ -11643,30 +11683,27 @@ float32 HELPER(recpe_f32)(float32 input, void *fpstp)
} else if (float32_is_zero(f32)) {
float_raise(float_flag_divbyzero, fpst);
return float32_set_sign(float32_infinity, float32_is_neg(f32));
- } else if ((f32_val & ~(1ULL << 31)) < (1ULL << 21)) {
+ } else if (float32_abs(f32) < (1ULL << 21)) {
/* Abs(value) < 2.0^-128 */
float_raise(float_flag_overflow | float_flag_inexact, fpst);
- if (round_to_inf(fpst, f32_sbit)) {
- return float32_set_sign(float32_infinity, float32_is_neg(f32));
+ if (round_to_inf(fpst, f32_sign)) {
+ return float32_set_sign(float32_infinity, f32_sign);
} else {
- return float32_set_sign(float32_maxnorm, float32_is_neg(f32));
+ return float32_set_sign(float32_maxnorm, f32_sign);
}
} else if (f32_exp >= 253 && fpst->flush_to_zero) {
float_raise(float_flag_underflow, fpst);
return float32_set_sign(float32_zero, float32_is_neg(f32));
}
+ f64_frac = call_recip_estimate(&f32_exp, 253,
+ ((uint64_t) f32_frac) << (52 - 23));
- f64 = make_float64(((int64_t)(f32_exp) << 52) | (int64_t)(f32_frac) << 29);
- r64 = call_recip_estimate(f64, 253, fpst);
- r64_val = float64_val(r64);
- r64_exp = extract64(r64_val, 52, 11);
- r64_frac = extract64(r64_val, 0, 52);
-
- /* result = sign : result_exp<7:0> : fraction<51:29>; */
- return make_float32(f32_sbit |
- (r64_exp & 0xff) << 23 |
- extract64(r64_frac, 29, 24));
+ /* result = sign : result_exp<7:0> : fraction<51:29> */
+ f32_val = deposit32(0, 31, 1, f32_sign);
+ f32_val = deposit32(f32_val, 23, 8, f32_exp);
+ f32_val = deposit32(f32_val, 0, 23, extract64(f64_frac, 52 - 23, 23));
+ return make_float32(f32_val);
}
float64 HELPER(recpe_f64)(float64 input, void *fpstp)
@@ -11674,12 +11711,9 @@ float64 HELPER(recpe_f64)(float64 input, void *fpstp)
float_status *fpst = fpstp;
float64 f64 = float64_squash_input_denormal(input, fpst);
uint64_t f64_val = float64_val(f64);
- uint64_t f64_sbit = 0x8000000000000000ULL & f64_val;
- int64_t f64_exp = extract64(f64_val, 52, 11);
- float64 r64;
- uint64_t r64_val;
- int64_t r64_exp;
- uint64_t r64_frac;
+ bool f64_sign = float64_is_neg(f64);
+ int f64_exp = extract64(f64_val, 52, 11);
+ uint64_t f64_frac = extract64(f64_val, 0, 52);
/* Deal with any special cases */
if (float64_is_any_nan(f64)) {
@@ -11700,25 +11734,23 @@ float64 HELPER(recpe_f64)(float64 input, void *fpstp)
} else if ((f64_val & ~(1ULL << 63)) < (1ULL << 50)) {
/* Abs(value) < 2.0^-1024 */
float_raise(float_flag_overflow | float_flag_inexact, fpst);
- if (round_to_inf(fpst, f64_sbit)) {
- return float64_set_sign(float64_infinity, float64_is_neg(f64));
+ if (round_to_inf(fpst, f64_sign)) {
+ return float64_set_sign(float64_infinity, f64_sign);
} else {
- return float64_set_sign(float64_maxnorm, float64_is_neg(f64));
+ return float64_set_sign(float64_maxnorm, f64_sign);
}
} else if (f64_exp >= 2045 && fpst->flush_to_zero) {
float_raise(float_flag_underflow, fpst);
return float64_set_sign(float64_zero, float64_is_neg(f64));
}
- r64 = call_recip_estimate(f64, 2045, fpst);
- r64_val = float64_val(r64);
- r64_exp = extract64(r64_val, 52, 11);
- r64_frac = extract64(r64_val, 0, 52);
+ f64_frac = call_recip_estimate(&f64_exp, 2045, f64_frac);
- /* result = sign : result_exp<10:0> : fraction<51:0> */
- return make_float64(f64_sbit |
- ((r64_exp & 0x7ff) << 52) |
- r64_frac);
+ /* result = sign : result_exp<10:0> : fraction<51:0>; */
+ f64_val = deposit64(0, 63, 1, f64_sign);
+ f64_val = deposit64(f64_val, 52, 11, f64_exp);
+ f64_val = deposit64(f64_val, 0, 52, f64_frac);
+ return make_float64(f64_val);
}
/* The algorithm that must be used to calculate the estimate
@@ -11907,19 +11939,17 @@ float64 HELPER(rsqrte_f64)(float64 input, void *fpstp)
uint32_t HELPER(recpe_u32)(uint32_t a, void *fpstp)
{
- float_status *s = fpstp;
- float64 f64;
+ /* float_status *s = fpstp; */
+ int input, estimate;
if ((a & 0x80000000) == 0) {
return 0xffffffff;
}
- f64 = make_float64((0x3feULL << 52)
- | ((int64_t)(a & 0x7fffffff) << 21));
-
- f64 = recip_estimate(f64, s);
+ input = extract32(a, 23, 9);
+ estimate = recip_estimate(input);
- return 0x80000000 | ((float64_val(f64) >> 21) & 0x7fffffff);
+ return deposit32(0, (32 - 9), 9, estimate);
}
uint32_t HELPER(rsqrte_u32)(uint32_t a, void *fpstp)