VCVTPS2PH—Convert Single-Precision FP value to 16-bit FP value

Opcode/Instruction Op/En 64/32-bit Mode CPUID Feature Flag Description

VEX.256.66.0F3A.W0 1D /r ib

VCVTPS2PH xmm1/m128, ymm2, imm8

 MR V/V F16C Convert eight packed single-precision floating-point value in ymm2 to packed half-precision (16-bit) floating-point value in xmm1/mem. Imm8 provides rounding controls.

VEX.128.66.0F3A.W0.1D /r ib

VCVTPS2PH xmm1/m64, xmm2, imm8

 MR V/V F16C Convert four packed single-precision float-ing-point value in xmm2 to packed half-precision (16-bit) floating-point value in xmm1/mem. Imm8 provides rounding con-trols.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
MR ModRM:r/m (w) ModRM:reg (r) NA NA

Description

Convert four or eight packed single-precision floating values in first source operand to four or eight packed half-precision (16-bit) floating-point values. The rounding mode is specified using the immediate field (imm8).

Underflow results (i.e. tiny results) are converted to denormals. MXCSR.FTZ is ignored. If a source element is denormal relative to input format with MXCSR.DAZ not set, DM masked and at least one of PM or UM unmasked; a SIMD exception will be raised with DE, UE and PE set.

128-bit version: The source operand is a XMM register. The destination operand is a XMM register or 64-bit memory location. The upper-bits vector register zeroing behavior of VEX prefix encoding still applies if the destination operand is a xmm register. So the upper bits (255:64) of corresponding YMM register are zeroed.

256-bit version: The source operand is a YMM register. The destination operand is a XMM register or 128-bit memory location. The upper-bits vector register zeroing behavior of VEX prefix encoding still applies if the destina-tion operand is a xmm register. So the upper bits (255:128) of the corresponding YMM register are zeroed.

Note: VEX.vvvv is reserved (must be 1111b).

The diagram below illustrates how data is converted from four packed single precision (in 128 bits) to four half precision (in 64 bits) FP values.

VCVTPS2PH xmm1/mem64, xmm2, imm8 127 96 95 64 63 32 31 0 VS3 VS2 VS1 VS0 xmm2 convert convert convert convert 127 96 95 64 63 48 47 32 31 16 15 0 VH3 VH2 VH1 VH0 xmm1/mem64

Figure 4-32. VCVTPS2PH (128-bit Version)

The immediate byte defines several bit fields that controls rounding operation. The effect and encoding of RC field are listed in Table 4-17.

Table 4-17. Immediate Byte Encoding for 16-bit Floating-Point Conversion Instructions

Bits Field Name/value Description Comment
Imm[1:0] RC=00B Round to nearest even If Imm[2] = 0
RC=01B Round down
RC=10B Round up
RC=11B Truncate
Imm[2] MS1=0 Use imm[1:0] for rounding Ignore MXCSR.RC
MS1=1 Use MXCSR.RC for rounding
Imm[7:3] Ignored Ignored by processor

Operation

vCvt_s2h(SRC1[31:0])
{
IF Imm[2] = 0
THEN // using Imm[1:0] for rounding control, see Table 4-17
          RETURN Cvt_Single_Precision_To_Half_Precision_FP_Imm(SRC1[31:0]);
ELSE // using MXCSR.RC for rounding control
          RETURN Cvt_Single_Precision_To_Half_Precision_FP_Mxcsr(SRC1[31:0]);
FI;
}

VCVTPS2PH (VEX.256 encoded version)

DEST[15:0] ← vCvt_s2h(SRC1[31:0]);
DEST[31:16] ← vCvt_s2h(SRC1[63:32]);
DEST[47:32] ← vCvt_s2h(SRC1[95:64]);
DEST[63:48] ← vCvt_s2h(SRC1[127:96]);
DEST[79:64] ← vCvt_s2h(SRC1[159:128]);
DEST[95:80] ← vCvt_s2h(SRC1[191:160]);
DEST[111:96] ← vCvt_s2h(SRC1[223:192]);
DEST[127:112] ← vCvt_s2h(SRC1[255:224]);
DEST[255:128] ← 0; // if DEST is a register

VCVTPS2PH (VEX.128 encoded version)

DEST[15:0] ← vCvt_s2h(SRC1[31:0]);
DEST[31:16] ← vCvt_s2h(SRC1[63:32]);
DEST[47:32] ← vCvt_s2h(SRC1[95:64]);
DEST[63:48] ← vCvt_s2h(SRC1[127:96]);
DEST[VLMAX-1:64] ←0; // if DEST is a register

Flags Affected

None

Intel C/C++ Compiler Intrinsic Equivalent

__m128i _mm_cvtps_ph ( __m128 m1, const int imm);

__m128i _mm256_cvtps_ph(__m256 m1, const int imm);

SIMD Floating-Point Exceptions

Invalid, Underflow, Overflow, Precision, Denormal (if MXCSR.DAZ=0);

Other Exceptions

Exceptions Type 11 (do not report #AC); additionally

#UD If VEX.W=1.