Neon equivalent to SSE intrinsics

Question

I'm trying to convert a c code to an optimized one using neon intrinsics.

Here is the c codes that operate over 2 operants not over vectors of operants.

uint16_t mult_z216(uint16_t a,uint16_t b){
unsigned int c1 = a*b;
    if(c1)
    {
        int c1h = c1 >> 16;
        int c1l = c1 & 0xffff;
        return (c1l - c1h + ((c1l<c1h)?1:0)) & 0xffff;
    }
    return (1-a-b) & 0xffff;
}

The SEE optimized version of this operation has already been implemented by the following:

#define MULT_Z216_SSE(a, b, c) \
    t0  = _mm_or_si128 ((a), (b)); \ //Computes the bitwise OR of the 128-bit value in a and the 128-bit value in b.
    (c) = _mm_mullo_epi16 ((a), (b)); \ //low 16-bits of the product of two 16-bit integers
    (a) = _mm_mulhi_epu16 ((a), (b)); \ //high 16-bits of the product of two 16-bit unsigned integers
    (b) = _mm_subs_epu16((c), (a)); \ //Subtracts the 8 unsigned 16-bit integers of a from the 8 unsigned 16-bit integers of c and saturates
    (b) = _mm_cmpeq_epi16 ((b), C_0x0_XMM); \ //Compares the 8 signed or unsigned 16-bit integers in a and the 8 signed or unsigned 16-bit integers in b for equality. (0xFFFF or 0x0)
    (b) = _mm_srli_epi16 ((b), 15); \ //shift right 16 bits
    (c) = _mm_sub_epi16 ((c), (a)); \ //Subtracts the 8 signed or unsigned 16-bit integers of b from the 8 signed or unsigned 16-bit integers of a.
    (a) = _mm_cmpeq_epi16 ((c), C_0x0_XMM); \ ////Compares the 8 signed or unsigned 16-bit integers in a and the 8 signed or unsigned 16-bit integers in b for equality. (0xFFFF or 0x0)
    (c) = _mm_add_epi16 ((c), (b)); \ // Adds the 8 signed or unsigned 16-bit integers in a to the 8 signed or unsigned 16-bit integers in b.
    t0  = _mm_and_si128 (t0, (a)); \ //Computes the bitwise AND of the 128-bit value in a and the 128-bit value in b.
    (c) = _mm_sub_epi16 ((c), t0); ///Subtracts the 8 signed or unsigned 16-bit integers of b from the 8 signed or unsigned 16-bit integers of a.

I've almost converted this one using neon intrinsics :

#define MULT_Z216_NEON(a, b, out) \
    temp = vorrq_u16 (*a, *b); \
    // ??
    // ??
    *b = vsubq_u16(*out, *a); \
    *b = vceqq_u16(*out, vdupq_n_u16(0x0000)); \
    *b = vshrq_n_u16(*b, 15); \
    *out = vsubq_s16(*out, *a); \
    *a = vceqq_s16(*c, vdupq_n_u16(0x0000)); \
    *c = vaddq_s16(*c, *b); \
    *temp = vandq_u16(*temp, *a); \
    *out = vsubq_s16(*out, *a);

I'm only missing the neon equivalents of _mm_mullo_epi16 ((a), (b)); and _mm_mulhi_epu16 ((a), (b));. Either I'm misunderstanding something or there is no such intrinsics in NEON. If there no equivalent how to archive theses steps using NEONS intrinsics ?

UPDATE :

I've forgot to emphasize the following point: the operants of the function are uint16x8_t NEON vectors (each element is a uint16_t => integers between 0 and 65535). In a answer someone proposed to use the intrinsic vqdmulhq_s16(). The use of this one won't match the given implementation because the multiplication intrinsic will interpret the vectors as signed values and produce a wrong output.

If you will have values > 32767 then you'll need to use the widening multiply suggested below (vmull_u16). If you know that your values will all be < 32768, then you can use vqdmulhq_s16. — BitBank

Guy Sirton Guy Sirton · Accepted Answer · 2012-07-02T18:30:50

You can use:

uint32x4_t vmull_u16 (uint16x4_t, uint16x4_t)

Which returns a vector of 32 bit products. If you want to break the result up into high and low parts you can use the NEON unzip intrinsic.

Neon equivalent to SSE intrinsics

2 Answers