VGETEXPPH - Convert Exponents of Packed FP16 Values to FP16 Values

Opcode/ Instruction

Op/ En

64/32 bit Mode Support

CPUID Feature Flag

Description

EVEX.128.66.MAP6.W0 42 /r VGETEXPPH xmm1{k1}{z}, xmm2/ m128/m16bcst

A

V/V

AVX512-FP16 AVX512VL

Convert the exponent of FP16 values in the source operand to FP16 results representing unbiased integer exponents and stores the results in the destination register subject to writemask k1.

EVEX.256.66.MAP6.W0 42 /r VGETEXPPH ymm1{k1}{z}, ymm2/ m256/m16bcst

A

V/V

AVX512-FP16 AVX512VL

Convert the exponent of FP16 values in the source operand to FP16 results representing unbiased integer exponents and stores the results in the destination register subject to writemask k1.

EVEX.512.66.MAP6.W0 42 /r VGETEXPPH zmm1{k1}{z}, zmm2/ m512/m16bcst {sae}

A

V/V

AVX512-FP16

Convert the exponent of FP16 values in the source operand to FP16 results representing unbiased integer exponents and stores the results in the destination register subject to writemask k1.

Instruction Operand Encoding

Op/En

Tuple

Operand 1

Operand 2

Operand 3

Operand 4

A

Full

ModRM:reg (w)

ModRM:r/m (r)

N/A

N/A

Description

This instruction extracts the biased exponents from the normalized FP16 representation of each word element of the source operand (the second operand) as unbiased signed integer value, or convert the denormal representa- tion of input data to unbiased negative integer values. Each integer value of the unbiased exponent is converted to an FP16 value and written to the corresponding word elements of the destination operand (the first operand) as FP16 numbers.

The destination elements are updated according to the writemask.

Each GETEXP operation converts the exponent value into a floating-point number (permitting input value in denormal representation). Special cases of input values are listed in Table 5-5.

The formula is:

GETEXP(x) = floor(log2(|x|)) Notation floor(x) stands for maximal integer not exceeding real number x.

Software usage of VGETEXPxx and VGETMANTxx instructions generally involve a combination of GETEXP operation and GETMANT operation (see VGETMANTPH). Thus, the VGETEXPPH instruction does not require software to handle SIMD floating-point exceptions.

Table 5-6. VGETEXPPH/VGETEXPSH Special Cases

Input Operand

Result

Comments

src1 = NaN

QNaN(src1)

0 < |src1| < INF

floor(log2(|src1|))

If (SRC = SNaN), then #IE. If (SRC = denormal), then #DE.

| src1| = +INF

+INF

| src1| = 0

-INF

Operation 

def normalize_exponent_tiny_fp16(src):
   jbit := 0
   // src & dst are FP16 numbers with sign(1b), exp(5b) and fraction (10b) fields
   dst.exp := 1                     // write bits 14:10
   dst.fraction := src.fraction // copy bits 9:0
   while jbit == 0:
       jbit := dst.fraction[9]         // msb of the fraction
       dst.fraction := dst.fraction << 1
       dst.exp := dst.exp - 1
   dst.fraction := 0
   return dst
def getexp_fp16(src):
   src.sign := 0                     // make positive
   exponent_all_ones := (src[14:10] == 0x1F)
   exponent_all_zeros := (src[14:10] == 0)
   mantissa_all_zeros := (src[9:0] == 0)
   zero := exponent_all_zeros and mantissa_all_zeros
   signaling_bit := src[9]
   nan := exponent_all_ones and not(mantissa_all_zeros)
   snan := nan and not(signaling_bit)
   qnan := nan and signaling_bit
   positive_infinity := not(negative) and exponent_all_ones and mantissa_all_zeros
   denormal := exponent_all_zeros and not(mantissa_all_zeros)
   if nan:
       if snan:
            MXCSR.IE := 1
       return qnan(src)             // convert snan to a qnan
   if positive_infinity:
       return src
   if zero:
       return -INF
   if denormal:
       tmp := normalize_exponent_tiny_fp16(src)
       MXCSR.DE := 1
   else:
       tmp := src
   tmp := SAR(tmp, 10)             // shift arithmetic right
   tmp := tmp - 15                  // subtract bias
   return convert_integer_to_fp16(tmp)

VGETEXPPH dest{k1}, src 

VL = 128, 256 or 512
KL := VL/16
FOR i := 0 to KL-1:
   IF k1[i] or *no writemask*:
       IF SRC is memory and (EVEX.b = 1):
            tsrc := src.fp16[0]
       ELSE:
            tsrc := src.fp16[i]
       DEST.fp16[i] := getexp_fp16(tsrc)
   ELSE IF *zeroing*:
       DEST.fp16[i] := 0
   //else DEST.fp16[i] remains unchanged
DEST[MAXVL-1:VL] := 0

Intel C/C++ Compiler Intrinsic Equivalent 

VGETEXPPH __m128h _mm_getexp_ph (__m128h a);
VGETEXPPH __m128h _mm_mask_getexp_ph (__m128h src, __mmask8 k, __m128h a);
VGETEXPPH __m128h _mm_maskz_getexp_ph (__mmask8 k, __m128h a);
VGETEXPPH __m256h _mm256_getexp_ph (__m256h a);
VGETEXPPH __m256h _mm256_mask_getexp_ph (__m256h src, __mmask16 k, __m256h a);
VGETEXPPH __m256h _mm256_maskz_getexp_ph (__mmask16 k, __m256h a);
VGETEXPPH __m512h _mm512_getexp_ph (__m512h a);
VGETEXPPH __m512h _mm512_mask_getexp_ph (__m512h src, __mmask32 k, __m512h a);
VGETEXPPH __m512h _mm512_maskz_getexp_ph (__mmask32 k, __m512h a);
VGETEXPPH __m512h _mm512_getexp_round_ph (__m512h a, const int sae);
VGETEXPPH __m512h _mm512_mask_getexp_round_ph (__m512h src, __mmask32 k, __m512h a, const int sae);
VGETEXPPH __m512h _mm512_maskz_getexp_round_ph (__mmask32 k, __m512h a, const int sae);

SIMD Floating-Point Exceptions

Invalid, Denormal.

Other Exceptions

EVEX-encoded instructions, see Table 2-46, "Type E2 Class Exception Conditions."