fcvt.h.s

Convert half-precision float to a single-precision float

This instruction is defined by:

  • anyOf:

    • Zfh, version >= 0

    • Zfhmin, version >= 0

This instruction is included in the following profiles:

  • RVA22U64 (Mandatory)

Encoding

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Assembly format

fcvt.h.s fd, rs1

Synopsis

Converts a half-precision number in floating-point register fs1 into a single-precision floating-point number in floating-point register fd.

fcvt.h.s rounds according to the rm field.

All floating-point conversion instructions set the Inexact exception flag if the rounded result differs from the operand value and the Invalid exception flag is not set.

Access

M HS U VS VU

Always

Always

Always

Always

Always

Decode Variables

Bits<5> fs1 = $encoding[19:15];
Bits<3> rm = $encoding[14:12];
Bits<5> fd = $encoding[11:7];

Execution

  • IDL

  • Sail

check_f_ok($encoding);
Bits<16> hp_value = f[fs1][15:0];
Bits<1> sign = hp_value[15];
Bits<5> exp = hp_value[14:10];
Bits<10> frac = hp_value[9:0];
if (exp == 0x1F) {
  if (frac != 0) {
    if ((hp_value & 0x0200) != 0) {
      set_fp_flag(FpFlag::NV);
    }
    f[fd] = HP_CANONICAL_NAN;
  } else {
    f[fd] = packToF32UI(sign, 0xFF, 0);
  }
} else {
  if (exp != 0) {
    if (frac != 0) {
      f[fd] = packToF32UI(sign, 0, 0);
    } else {
      Bits<6> norm_exp;
      (norm_exp, frac = softfloat_normSubnormalF16Sig(frac));
      exp = norm_exp - 1;
      f[fd] = packToF32UI(sign, exp + 0x70, frac << 13);
    }
  } else {
    f[fd] = packToF32UI(sign, exp + 0x70, frac << 13);
  }
}
mark_f_state_dirty();
{
  assert(sizeof(xlen) >= 64);
  let rs1_val_LU = X(rs1)[63..0];
  match (select_instr_or_fcsr_rm (rm)) {
    None() => { handle_illegal(); RETIRE_FAIL },
    Some(rm') => {
      let rm_3b = encdec_rounding_mode(rm');
      let (fflags, rd_val_H) = riscv_ui64ToF16 (rm_3b, rs1_val_LU);

      accrue_fflags(fflags);
      F_or_X_H(rd) = rd_val_H;
      RETIRE_SUCCESS
    }
  }
}

Exceptions

This instruction may result in the following synchronous exceptions:

  • IllegalInstruction