Now use the same algorithm as described in the ARM ARM.
Signed-off-by: Christophe Lyon <christophe.l...@st.com>
---
target-arm/helper.c | 72 ++++++++++++++++++++++++++++++++++++++++++--------
1 files changed, 60 insertions(+), 12 deletions(-)
diff --git a/target-arm/helper.c b/target-arm/helper.c
index 7f63a28..1ab5ae9 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -2687,13 +2687,53 @@ float32 HELPER(rsqrts_f32)(float32 a, float32 b,
CPUState *env)
/* NEON helpers. */
-/* TODO: The architecture specifies the value that the estimate functions
- should return. We return the exact reciprocal/root instead. */
-float32 HELPER(recpe_f32)(float32 a, CPUState *env)
+/* The algorithm that must be used to calculate the estimate
+ * is specified by the ARM ARM.
+ */
+static float64 recip_estimate(float64 a, CPUState *env)
{
float_status *s = &env->vfp.fp_status;
- float32 one = int32_to_float32(1, s);
- return float32_div(one, a, s);
+ float64 one = int64_to_float64(1, s);
+ /* q = (int)(a * 512.0) */
+ float64 x512 = int64_to_float64(512, s);
+ float64 q = float64_mul(x512, 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);
+ float64 half = float64_div(one, int64_to_float64(2, s), s);
+ q = float64_add(q, half, s);
+ q = float64_div(q, x512, s);
+ q = float64_div(one, q, s);
+
+ /* s = (int)(256.0 * r + 0.5) */
+ q = float64_mul(q, int64_to_float64(256, s), s);
+ q = float64_add(q, half, s);
+ q_int = float64_to_int64_round_to_zero(q, s);
+
+ /* return (double)s / 256.0 */
+ return float64_div(int64_to_float64(q_int, s), int64_to_float64(256, s),
s);
+}
+
+/* TODO: handle NaNs, zero and infinity as special input values. */
+float32 HELPER(recpe_f32)(float32 a, CPUState *env)
+{
+ float64 f64;
+ uint32_t val32;
+
+ int result_exp;
+
+ f64 = make_float64(((int64_t)0x3FE << 52)
+ | ((int64_t)(float32_val(a) & 0x7FFFFF) << 29));
+
+ result_exp = 253 - ((float32_val(a) & 0x7F800000) >> 23);
+
+ f64 = recip_estimate(f64, env);
+
+ val32 = (float32_val(a) & 0x80000000)
+ | ((result_exp & 0xFF) << 23)
+ | ((float64_val(f64) >> 29) & 0x7FFFFF);
+ return make_float32(val32);
}
float32 HELPER(rsqrte_f32)(float32 a, CPUState *env)
@@ -2705,13 +2745,21 @@ float32 HELPER(rsqrte_f32)(float32 a, CPUState *env)
uint32_t HELPER(recpe_u32)(uint32_t a, CPUState *env)
{
- float_status *s = &env->vfp.fp_status;
- float32 tmp;
- tmp = int32_to_float32(a, s);
- tmp = float32_scalbn(tmp, -32, s);
- tmp = helper_recpe_f32(tmp, env);
- tmp = float32_scalbn(tmp, 31, s);
- return float32_to_int32(tmp, s);
+ union {
+ int64_t i;
+ float64 f;
+ } dp_operand;
+
+ if ((a & 0x80000000) == 0) {
+ return 0xFFFFFFFF;
+ }
+
+ dp_operand.i = ((int64_t)0x3FE << 52)
+ | ((int64_t)(a & 0x7FFFFFFF) << 21);
+
+ dp_operand.f = recip_estimate (dp_operand.f, env);
+
+ return 0x80000000 | ((dp_operand.i >> 21) & 0x7FFFFFFF);
}
uint32_t HELPER(rsqrte_u32)(uint32_t a, CPUState *env)
--
1.7.2.3
