target/riscv: rvv-1.0: floating-point reciprocal estimate instruction

Implement the floating-point reciprocal estimate to 7 bits instruction.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-71-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

4 files changed, 197 insertions, 0 deletions

diff --git a/target/riscv/helper.h b/target/riscv/helper.h
index bdf06dfb24..ab283d12b7 100644
--- a/target/riscv/helper.h
+++ b/target/riscv/helper.h
@@ -845,6 +845,10 @@ DEF_HELPER_5(vfrsqrt7_v_h, void, ptr, ptr, ptr, env, i32)
 DEF_HELPER_5(vfrsqrt7_v_w, void, ptr, ptr, ptr, env, i32)
 DEF_HELPER_5(vfrsqrt7_v_d, void, ptr, ptr, ptr, env, i32)
 
+DEF_HELPER_5(vfrec7_v_h, void, ptr, ptr, ptr, env, i32)
+DEF_HELPER_5(vfrec7_v_w, void, ptr, ptr, ptr, env, i32)
+DEF_HELPER_5(vfrec7_v_d, void, ptr, ptr, ptr, env, i32)
+
 DEF_HELPER_6(vfmin_vv_h, void, ptr, ptr, ptr, ptr, env, i32)
 DEF_HELPER_6(vfmin_vv_w, void, ptr, ptr, ptr, ptr, env, i32)
 DEF_HELPER_6(vfmin_vv_d, void, ptr, ptr, ptr, ptr, env, i32)
diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
index 6e5f288943..952768f8de 100644
--- a/target/riscv/insn32.decode
+++ b/target/riscv/insn32.decode
@@ -561,6 +561,7 @@ vfwnmsac_vv     111111 . ..... ..... 001 ..... 1010111 @r_vm
 vfwnmsac_vf     111111 . ..... ..... 101 ..... 1010111 @r_vm
 vfsqrt_v        010011 . ..... 00000 001 ..... 1010111 @r2_vm
 vfrsqrt7_v      010011 . ..... 00100 001 ..... 1010111 @r2_vm
+vfrec7_v        010011 . ..... 00101 001 ..... 1010111 @r2_vm
 vfmin_vv        000100 . ..... ..... 001 ..... 1010111 @r_vm
 vfmin_vf        000100 . ..... ..... 101 ..... 1010111 @r_vm
 vfmax_vv        000110 . ..... ..... 001 ..... 1010111 @r_vm
diff --git a/target/riscv/insn_trans/trans_rvv.c.inc b/target/riscv/insn_trans/trans_rvv.c.inc
index 8fe718610a..ff8f6df8f7 100644
--- a/target/riscv/insn_trans/trans_rvv.c.inc
+++ b/target/riscv/insn_trans/trans_rvv.c.inc
@@ -2408,6 +2408,7 @@ static bool trans_##NAME(DisasContext *s, arg_rmr *a)  \
 
 GEN_OPFV_TRANS(vfsqrt_v, opfv_check, RISCV_FRM_DYN)
 GEN_OPFV_TRANS(vfrsqrt7_v, opfv_check, RISCV_FRM_DYN)
+GEN_OPFV_TRANS(vfrec7_v, opfv_check, RISCV_FRM_DYN)
 
 /* Vector Floating-Point MIN/MAX Instructions */
 GEN_OPFVV_TRANS(vfmin_vv, opfvv_check)
diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
index d5f3229bcb..946dca53ff 100644
--- a/target/riscv/vector_helper.c
+++ b/target/riscv/vector_helper.c
@@ -3587,6 +3587,197 @@ GEN_VEXT_V_ENV(vfrsqrt7_v_h, 2, 2)
 GEN_VEXT_V_ENV(vfrsqrt7_v_w, 4, 4)
 GEN_VEXT_V_ENV(vfrsqrt7_v_d, 8, 8)
 
+/*
+ * Vector Floating-Point Reciprocal Estimate Instruction
+ *
+ * Adapted from riscv-v-spec recip.c:
+ * https://github.com/riscv/riscv-v-spec/blob/master/recip.c
+ */
+static uint64_t frec7(uint64_t f, int exp_size, int frac_size,
+                      float_status *s)
+{
+    uint64_t sign = extract64(f, frac_size + exp_size, 1);
+    uint64_t exp = extract64(f, frac_size, exp_size);
+    uint64_t frac = extract64(f, 0, frac_size);
+
+    const uint8_t lookup_table[] = {
+        127, 125, 123, 121, 119, 117, 116, 114,
+        112, 110, 109, 107, 105, 104, 102, 100,
+        99, 97, 96, 94, 93, 91, 90, 88,
+        87, 85, 84, 83, 81, 80, 79, 77,
+        76, 75, 74, 72, 71, 70, 69, 68,
+        66, 65, 64, 63, 62, 61, 60, 59,
+        58, 57, 56, 55, 54, 53, 52, 51,
+        50, 49, 48, 47, 46, 45, 44, 43,
+        42, 41, 40, 40, 39, 38, 37, 36,
+        35, 35, 34, 33, 32, 31, 31, 30,
+        29, 28, 28, 27, 26, 25, 25, 24,
+        23, 23, 22, 21, 21, 20, 19, 19,
+        18, 17, 17, 16, 15, 15, 14, 14,
+        13, 12, 12, 11, 11, 10, 9, 9,
+        8, 8, 7, 7, 6, 5, 5, 4,
+        4, 3, 3, 2, 2, 1, 1, 0
+    };
+    const int precision = 7;
+
+    if (exp == 0 && frac != 0) { /* subnormal */
+        /* Normalize the subnormal. */
+        while (extract64(frac, frac_size - 1, 1) == 0) {
+            exp--;
+            frac <<= 1;
+        }
+
+        frac = (frac << 1) & MAKE_64BIT_MASK(0, frac_size);
+
+        if (exp != 0 && exp != UINT64_MAX) {
+            /*
+             * Overflow to inf or max value of same sign,
+             * depending on sign and rounding mode.
+             */
+            s->float_exception_flags |= (float_flag_inexact |
+                                         float_flag_overflow);
+
+            if ((s->float_rounding_mode == float_round_to_zero) ||
+                ((s->float_rounding_mode == float_round_down) && !sign) ||
+                ((s->float_rounding_mode == float_round_up) && sign)) {
+                /* Return greatest/negative finite value. */
+                return (sign << (exp_size + frac_size)) |
+                    (MAKE_64BIT_MASK(frac_size, exp_size) - 1);
+            } else {
+                /* Return +-inf. */
+                return (sign << (exp_size + frac_size)) |
+                    MAKE_64BIT_MASK(frac_size, exp_size);
+            }
+        }
+    }
+
+    int idx = frac >> (frac_size - precision);
+    uint64_t out_frac = (uint64_t)(lookup_table[idx]) <<
+                            (frac_size - precision);
+    uint64_t out_exp = 2 * MAKE_64BIT_MASK(0, exp_size - 1) + ~exp;
+
+    if (out_exp == 0 || out_exp == UINT64_MAX) {
+        /*
+         * The result is subnormal, but don't raise the underflow exception,
+         * because there's no additional loss of precision.
+         */
+        out_frac = (out_frac >> 1) | MAKE_64BIT_MASK(frac_size - 1, 1);
+        if (out_exp == UINT64_MAX) {
+            out_frac >>= 1;
+            out_exp = 0;
+        }
+    }
+
+    uint64_t val = 0;
+    val = deposit64(val, 0, frac_size, out_frac);
+    val = deposit64(val, frac_size, exp_size, out_exp);
+    val = deposit64(val, frac_size + exp_size, 1, sign);
+    return val;
+}
+
+static float16 frec7_h(float16 f, float_status *s)
+{
+    int exp_size = 5, frac_size = 10;
+    bool sign = float16_is_neg(f);
+
+    /* frec7(+-inf) = +-0 */
+    if (float16_is_infinity(f)) {
+        return float16_set_sign(float16_zero, sign);
+    }
+
+    /* frec7(+-0) = +-inf */
+    if (float16_is_zero(f)) {
+        s->float_exception_flags |= float_flag_divbyzero;
+        return float16_set_sign(float16_infinity, sign);
+    }
+
+    /* frec7(sNaN) = canonical NaN */
+    if (float16_is_signaling_nan(f, s)) {
+        s->float_exception_flags |= float_flag_invalid;
+        return float16_default_nan(s);
+    }
+
+    /* frec7(qNaN) = canonical NaN */
+    if (float16_is_quiet_nan(f, s)) {
+        return float16_default_nan(s);
+    }
+
+    /* +-normal, +-subnormal */
+    uint64_t val = frec7(f, exp_size, frac_size, s);
+    return make_float16(val);
+}
+
+static float32 frec7_s(float32 f, float_status *s)
+{
+    int exp_size = 8, frac_size = 23;
+    bool sign = float32_is_neg(f);
+
+    /* frec7(+-inf) = +-0 */
+    if (float32_is_infinity(f)) {
+        return float32_set_sign(float32_zero, sign);
+    }
+
+    /* frec7(+-0) = +-inf */
+    if (float32_is_zero(f)) {
+        s->float_exception_flags |= float_flag_divbyzero;
+        return float32_set_sign(float32_infinity, sign);
+    }
+
+    /* frec7(sNaN) = canonical NaN */
+    if (float32_is_signaling_nan(f, s)) {
+        s->float_exception_flags |= float_flag_invalid;
+        return float32_default_nan(s);
+    }
+
+    /* frec7(qNaN) = canonical NaN */
+    if (float32_is_quiet_nan(f, s)) {
+        return float32_default_nan(s);
+    }
+
+    /* +-normal, +-subnormal */
+    uint64_t val = frec7(f, exp_size, frac_size, s);
+    return make_float32(val);
+}
+
+static float64 frec7_d(float64 f, float_status *s)
+{
+    int exp_size = 11, frac_size = 52;
+    bool sign = float64_is_neg(f);
+
+    /* frec7(+-inf) = +-0 */
+    if (float64_is_infinity(f)) {
+        return float64_set_sign(float64_zero, sign);
+    }
+
+    /* frec7(+-0) = +-inf */
+    if (float64_is_zero(f)) {
+        s->float_exception_flags |= float_flag_divbyzero;
+        return float64_set_sign(float64_infinity, sign);
+    }
+
+    /* frec7(sNaN) = canonical NaN */
+    if (float64_is_signaling_nan(f, s)) {
+        s->float_exception_flags |= float_flag_invalid;
+        return float64_default_nan(s);
+    }
+
+    /* frec7(qNaN) = canonical NaN */
+    if (float64_is_quiet_nan(f, s)) {
+        return float64_default_nan(s);
+    }
+
+    /* +-normal, +-subnormal */
+    uint64_t val = frec7(f, exp_size, frac_size, s);
+    return make_float64(val);
+}
+
+RVVCALL(OPFVV1, vfrec7_v_h, OP_UU_H, H2, H2, frec7_h)
+RVVCALL(OPFVV1, vfrec7_v_w, OP_UU_W, H4, H4, frec7_s)
+RVVCALL(OPFVV1, vfrec7_v_d, OP_UU_D, H8, H8, frec7_d)
+GEN_VEXT_V_ENV(vfrec7_v_h, 2, 2)
+GEN_VEXT_V_ENV(vfrec7_v_w, 4, 4)
+GEN_VEXT_V_ENV(vfrec7_v_d, 8, 8)
+
 /* Vector Floating-Point MIN/MAX Instructions */
 RVVCALL(OPFVV2, vfmin_vv_h, OP_UUU_H, H2, H2, H2, float16_minimum_number)
 RVVCALL(OPFVV2, vfmin_vv_w, OP_UUU_W, H4, H4, H4, float32_minimum_number)