UCVTF (scalar, fixed-point)

Unsigned fixed-point convert to floating-point (scalar)

This instruction converts the unsigned value in the 32-bit or 64-bit general-purpose source register to a floating-point value using the rounding mode that is specified by the FPCR, and writes the result to the SIMD&FP destination register.

This instruction can generate a floating-point exception. Depending on the settings in FPCR, the exception results in either a flag being set in FPSR or a synchronous exception being generated. For more information, see Floating-point exceptions and exception traps.

Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

Encoding: Floating-point

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
	0	0	1	1	1	1	0			0	0	0	0	1	1
sf		S						ftype			rmode		opcode			scale						Rn					Rd

32-bit to half-precision (sf == 0 && ftype == 11)

UCVTF <Hd>, <Wn>, #<fbits>

64-bit to half-precision (sf == 1 && ftype == 11)

UCVTF <Hd>, <Xn>, #<fbits>

32-bit to single-precision (sf == 0 && ftype == 00)

UCVTF <Sd>, <Wn>, #<fbits>

64-bit to single-precision (sf == 1 && ftype == 00)

UCVTF <Sd>, <Xn>, #<fbits>

32-bit to double-precision (sf == 0 && ftype == 01)

UCVTF <Dd>, <Wn>, #<fbits>

64-bit to double-precision (sf == 1 && ftype == 01)

UCVTF <Dd>, <Xn>, #<fbits>

Decoding algorithm

if !IsFeatureImplemented(FEAT_FP) then EndOfDecode(Decode_UNDEF);
if ftype == '10' then EndOfDecode(Decode_UNDEF);
if ftype == '11' && !IsFeatureImplemented(FEAT_FP16) then EndOfDecode(Decode_UNDEF);
if sf == '0' && scale<5> == '0' then EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);

constant integer intsize = 32 << UInt(sf);
constant integer decode_fltsize = 8 << UInt(ftype EOR '10');

constant integer fracbits = 64 - UInt(scale);

constant boolean unsigned = TRUE;

Operation

CheckFPEnabled64();

constant boolean merge = IsMerging(FPCR);
constant integer fltsize = if merge then 128 else decode_fltsize;
bits(fltsize) fltval = if merge then V[d, fltsize] else Zeros(fltsize);
constant bits(intsize) intval = X[n, intsize];
constant FPRounding rounding = FPRoundingMode(FPCR);

Elem[fltval, 0, decode_fltsize] = FixedToFP(intval, fracbits, unsigned,
                                            FPCR, rounding, decode_fltsize);

V[d, fltsize] = fltval;

Explanations

<Hd>: Is the 16-bit name of the SIMD&FP destination register, encoded in the "Rd" field.
<Wn>: Is the 32-bit name of the general-purpose source register, encoded in the "Rn" field.
<fbits>: For the "32-bit to double-precision", "32-bit to half-precision", and "32-bit to single-precision" variants: is the number of bits after the binary point in the fixed-point source, in the range 1 to 32, encoded as 64 minus "scale".
<fbits>: For the "64-bit to double-precision", "64-bit to half-precision", and "64-bit to single-precision" variants: is the number of bits after the binary point in the fixed-point source, in the range 1 to 64, encoded as 64 minus "scale".
<Xn>: Is the 64-bit name of the general-purpose source register, encoded in the "Rn" field.
<Sd>: Is the 32-bit name of the SIMD&FP destination register, encoded in the "Rd" field.
<Dd>: Is the 64-bit name of the SIMD&FP destination register, encoded in the "Rd" field.