OpenBLAS/kernel/power/isamax.c

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#include "common.h"
#include <math.h>
#include <altivec.h>


#if defined(DOUBLE)
    #define ABS fabs
#else
    #define ABS fabsf
#endif

/**
 * Find  maximum index 
 * Warning: requirements n>0  and n % 64 == 0
 * @param n     
 * @param x     pointer to the vector
 * @param maxf  (out) maximum absolute value .( only for output )
 * @return  index 
 */
static BLASLONG siamax_kernel_64(BLASLONG n, FLOAT *x, FLOAT *maxf) {
    BLASLONG index;
    BLASLONG i=0;
    register __vector unsigned int static_index0 = {0,1,2,3};
    register __vector unsigned int temp0 = {4,4,4, 4}; //temporary vector register
    register __vector unsigned int temp1=  temp0<<1;  //{8,8,8,8}
    register __vector unsigned int static_index1=static_index0 +temp0;//{4,5,6,7};
    register __vector unsigned int static_index2=static_index0 +temp1;//{8,9,10,11};
    register __vector unsigned int static_index3=static_index1 +temp1; //{12,13,14,15};
    temp0=vec_xor(temp0,temp0);
    temp1=temp1 <<1 ; //{16,16,16,16}
    register __vector unsigned int quadruple_indices=temp0;//{0,0,0,0}
    register __vector float quadruple_values={0,0,0,0};
    register __vector float * v_ptrx=(__vector float *)x;
    for(; i<n; i+=64){
       //absolute temporary vectors
       register __vector float v0=vec_abs(v_ptrx[0]);
       register __vector float v1=vec_abs(v_ptrx[1]);
       register __vector float v2=vec_abs(v_ptrx[2]);
       register __vector float v3=vec_abs(v_ptrx[3]);
       register __vector float v4=vec_abs(v_ptrx[4]);
       register __vector float v5=vec_abs(v_ptrx[5]);
       register __vector float v6=vec_abs(v_ptrx[6]);       
       register __vector float v7=vec_abs(v_ptrx[7]);
       //cmp quadruple pairs
       register __vector bool int r1=vec_cmpgt(v1,v0);
       register __vector bool int r2=vec_cmpgt(v3,v2);
       register __vector bool int r3=vec_cmpgt(v5,v4);
       register __vector bool int r4=vec_cmpgt(v7,v6);
      
       //select
       register __vector unsigned int ind0_first= vec_sel(static_index0,static_index1,r1);
       register __vector float vf0= vec_sel(v0,v1,r1);

       register __vector unsigned int ind1= vec_sel(static_index2,static_index3,r2);
       register __vector float vf1= vec_sel(v2,v3,r2);

       register __vector unsigned int ind2= vec_sel(static_index0,static_index1,r3);
       v0=vec_sel(v4,v5,r3);

       register __vector unsigned int ind3= vec_sel(static_index2,static_index3,r4);
       v1=vec_sel(v6,v7,r4);

       // cmp selected
        r1=vec_cmpgt(vf1,vf0);
       r2=vec_cmpgt(v1,v0);

       v_ptrx+=8;
       //select from above 
       ind0_first= vec_sel(ind0_first,ind1,r1);
       vf0= vec_sel(vf0,vf1,r1) ;

       ind2= vec_sel(ind2,ind3,r2);
       vf1= vec_sel(v0,v1,r2);

       //second indices actually should be within [16,31] so ind2+16
       ind2 +=temp1;
       
       //final cmp and select index and value for the first 32 values
       r1=vec_cmpgt(vf1,vf0);
       ind0_first = vec_sel(ind0_first,ind2,r1);
       vf0= vec_sel(vf0,vf1,r1);
 
       ind0_first+=temp0; //get absolute index

       temp0+=temp1;
       temp0+=temp1; //temp0+32
       //second part of 32
       // absolute temporary vectors
       v0=vec_abs(v_ptrx[0]);
       v1=vec_abs(v_ptrx[1]);
       v2=vec_abs(v_ptrx[2]);
       v3=vec_abs(v_ptrx[3]);
       v4=vec_abs(v_ptrx[4]);
       v5=vec_abs(v_ptrx[5]);
       v6=vec_abs(v_ptrx[6]);       
       v7=vec_abs(v_ptrx[7]);
       //cmp quadruple pairs
       r1=vec_cmpgt(v1,v0);
       r2=vec_cmpgt(v3,v2);
       r3=vec_cmpgt(v5,v4);
       r4=vec_cmpgt(v7,v6);
       //select
       register __vector unsigned int ind0_second= vec_sel(static_index0,static_index1,r1);
       register __vector float vv0= vec_sel(v0,v1,r1);

       ind1= vec_sel(static_index2,static_index3,r2);
       register __vector float vv1= vec_sel(v2,v3,r2);

       ind2= vec_sel(static_index0,static_index1,r3);
       v0=vec_sel(v4,v5,r3);

       ind3= vec_sel(static_index2,static_index3,r4);
       v1=vec_sel(v6,v7,r4);

       // cmp selected
       r1=vec_cmpgt(vv1,vv0);
       r2=vec_cmpgt(v1,v0);

       v_ptrx+=8;
       //select from above 
       ind0_second= vec_sel(ind0_second,ind1,r1);
       vv0= vec_sel(vv0,vv1,r1) ;

       ind2= vec_sel(ind2,ind3,r2);
       vv1= vec_sel(v0,v1,r2) ;  

       //second indices actually should be within [16,31] so ind2+16
       ind2 +=temp1;
       
       //final cmp and select index and value for the second 32 values
       r1=vec_cmpgt(vv1,vv0);
       ind0_second = vec_sel(ind0_second,ind2,r1);
       vv0= vec_sel(vv0,vv1,r1);

       ind0_second+=temp0; //get absolute index
    
       //find final quadruple from 64 elements
       r2=vec_cmpgt(vv0,vf0);
       ind2 = vec_sel( ind0_first,ind0_second,r2);
       vv0= vec_sel(vf0,vv0,r2);       

       //compare with old quadruple and update 
       r3=vec_cmpgt(vv0,quadruple_values);
       quadruple_indices = vec_sel( quadruple_indices,ind2,r3);
       quadruple_values= vec_sel(quadruple_values,vv0,r3);      

       temp0+=temp1;
       temp0+=temp1; //temp0+32
 
    }

    //now we have to chose from 4 values and 4 different indices
    // we will compare pairwise if pairs are exactly the same we will choose minimum between index
    // otherwise we will assign index of the maximum value
    float a1,a2,a3,a4;
    unsigned int i1,i2,i3,i4;
    a1=vec_extract(quadruple_values,0);
    a2=vec_extract(quadruple_values,1);
    a3=vec_extract(quadruple_values,2);
    a4=vec_extract(quadruple_values,3);
    i1=vec_extract(quadruple_indices,0);
    i2=vec_extract(quadruple_indices,1);
    i3=vec_extract(quadruple_indices,2);
    i4=vec_extract(quadruple_indices,3);
    if(a1==a2){
      index=i1>i2?i2:i1;
    }else if(a2>a1){
      index=i2;
      a1=a2;
    }else{
       index= i1;
    }

    if(a4==a3){
      i1=i3>i4?i4:i3;
    }else if(a4>a3){
      i1=i4;
      a3=a4;
    }else{
       i1= i3;
    }

    if(a1==a3){
       index=i1>index?index:i1;
       *maxf=a1; 
    }else if(a3>a1){
       index=i1;
       *maxf=a3;
    }else{ 
        *maxf=a1;
    }
    return index;

}

BLASLONG CNAME(BLASLONG n, FLOAT *x, BLASLONG inc_x) {
    BLASLONG i = 0;
    BLASLONG j = 0;
    FLOAT maxf = 0.0;
    BLASLONG max = 0;

    if (n <= 0 || inc_x <= 0) return (max);

    if (inc_x == 1) {

        BLASLONG n1 = n & -64;
        if (n1 > 0) {

            max = siamax_kernel_64(n1, x, &maxf);

            i = n1;
        }

        while (i < n) {
            if (ABS(x[i]) > maxf) {
                max = i;
                maxf = ABS(x[i]);
            }
            i++;
        }
        return (max + 1);

    } else {

        BLASLONG n1 = n & -4;
        while (j < n1) {

            if (ABS(x[i]) > maxf) {
                max = j;
                maxf = ABS(x[i]);
            }
            if (ABS(x[i + inc_x]) > maxf) {
                max = j + 1;
                maxf = ABS(x[i + inc_x]);
            }
            if (ABS(x[i + 2 * inc_x]) > maxf) {
                max = j + 2;
                maxf = ABS(x[i + 2 * inc_x]);
            }
            if (ABS(x[i + 3 * inc_x]) > maxf) {
                max = j + 3;
                maxf = ABS(x[i + 3 * inc_x]);
            }

            i += inc_x * 4;

            j += 4;

        }


        while (j < n) {
            if (ABS(x[i]) > maxf) {
                max = j;
                maxf = ABS(x[i]);
            }
            i += inc_x;
            j++;
        }
        return (max + 1);
    }
}