#size scalar altivec
13 5 2
16 6 1
27 12 3
64 23 2
90 29 3
128 43 3
185 59 5
256 81 6
347 111 8
512 164 11
831 277 18
2048 686 40
3981 1316 86

#include <altivec.h>
#include <stdio.h>
#include <time.h>

// This one was shamelessy stolen and adapted from Apple's Altivec tutorial
vector unsigned char inline vec_ldsplatchar(unsigned char splatchar) {

vector unsigned char splatmap = vec_lvsl(0, &splatchar);
vector unsigned char result = vec_lde(0, &splatchar);

splatmap = vec_splat(splatmap, 0);

return vec_perm(result, result, splatmap);
}

unsigned char *vec_strfill(unsigned char *s, int len, char p) {
int i;
vector unsigned char sm = vec_ldsplatchar(p);
vector unsigned char *v1 = (vector unsigned char *)s;

vector unsigned char vec_a;
for (i=0; i < len-1; i = i+16) {
vec_a = vec_ld(0, v1);
vec_a = vec_splat(sm, 0);
vec_st(vec_a, i, s);
}

return s;
}

unsigned char *strfill(unsigned char *s, int len,char fill)
{
while (len--) *s++ = fill;
*(s) = '\0';
return(s);
} /* strfill */


int main( void )
{
int i, j, k, max, loops = 100000000;
time_t dt1, dt2, t1, t0;
int sizes[] = {13,16,27,64,90,128,185,256,347,512,831,2048,3981,8192,10000};

printf("#size\tscalar\taltivec\n");
for (k = 0; k < 16; k++) {
max = sizes[k];
unsigned char __attribute__ ((aligned(16))) test[max];
unsigned char __attribute__ ((aligned(16))) splatchar = rand();

t0 = time(NULL);
for (j=0; j < loops; j++) {
test[max] = '\0';
strfill(test, max, splatchar);
}
t1 = time(NULL);
dt1 = t1 - t0;

t0 = time(NULL);
for (j=0; j < loops; j++) {
vec_strfill(test, max, splatchar);
}
t1 = time(NULL);
dt2 = t1 - t0;
printf("%ld\t%ld\t%ld\n", max, dt1, dt2);
}
return 0;
}

/* All AltiVec loads and stores silently round down their addresses to a
multiple of 16. Handling of arbitrary string buffers must take that into
account.

general case: partial vector at start and end of string

|.....--+-------+-------+-----..|

so we must handle a partial vector first, then a number of whole vectors,
and another partial vector at the end

special case: first and last char of string within same vector

|.----..|

partial vectors are handled by loading the original value, merging in the
modified bytes with vec_sel, and storing back the modified vector
*/
unsigned char *vec_strfill(unsigned char *s, int len, char p) {
unsigned char* ptrlast = s + (len - 1);
unsigned char* ptrfirst = s;

// for inline char -> vector char conversion
union {
vector unsigned char v;
unsigned char c[16];
} envelope;
envelope.c[0] = p;

// this code fails for len <= 0 when first and last positions are in
// different vectors, but that is an undefined case anyway
assert (len > 0);

// these maske are 0xff where we want to modify chars in memory, 0 otherwise
// (vec_lvsr creates a vector value based on the address alignment; these are
// usually used with vec_perm, but I compare them to a threshold value to
// create a mask vector of 0xff/0x00 chars)
vector unsigned char firstmask;
firstmask = (vector unsigned char) vec_cmpgt(vec_lvsr(0, ptrfirst),
vec_splat_u8(15));
// (the type cast works around a bug in Apple GCC)

// vec_splat can only take values from -16 to +15, so I have to build the
// needed value 17 manually (vec_splat_u8(15) is a common subexpression)
vector unsigned char lastmask;
lastmask = (vector unsigned char) vec_cmplt(vec_lvsr(0, ptrlast),
vec_add(vec_splat_u8(15),
vec_splat_u8(2)));
// (the type cast works around a bug in Apple GCC)

// build a vector full of fill chars
vector unsigned char fillchar = vec_splat(envelope.v, 0);

// first and last chars in same vector? (xor used as bit-wise compare)
if ((((long)ptrlast ^ (long)ptrfirst) & ~15L) == 0) {

firstmask = vec_and(firstmask, lastmask); // simply combine masks

// read, modify (based on mask), write
vec_st(vec_sel(vec_ld(0, ptrfirst), fillchar, firstmask), 0, ptrfirst);

return s;
}

// handle first vector: read, modify (based on mask), write
vec_st(vec_sel(vec_ld(0, ptrfirst), fillchar, firstmask), 0, ptrfirst);
// it can happen that firstmask is all 0xff, so it might pay off to test
// whether s is aligned and go directly to the while() loop

// reduce remaining length by the amount of chars covered by first vector
len -= 16 - ((int)ptrfirst & 15);

// now store a number of aligned vectors
while (len >= 16) {
vec_st(fillchar, 0, ptrfirst);
ptrfirst += 16;
len -= 16;
}

// finally there might be a last partial vector
// (if lastmask is all 0xff, then len is already zero here)
if (len > 0) {
// read, modify (based on mask), write
vec_st(vec_sel(vec_ld(0, ptrlast), fillchar, lastmask), 0, ptrlast);
}

return s;
}

#define vec_strfill_libmoto(s, len, p) ((unsigned char *)memset(s, p, len))

if ( strcmp(test1, test2) == 0) {
printf("test1 = test2)\n");
}
if ( strcmp(test1, test3) == 0) {
printf("test1 = test3)\n");
}
if ( strcmp(test1, test4) == 0) {
printf("test1 = test4)\n");
}
if ( strcmp(test2, test3) == 0) {
printf("test2 = test3)\n");
}
if ( strcmp(test2, test4) == 0) {
printf("test2 = test4)\n");
}
if ( strcmp(test3, test4) == 0) {
printf("test3 = test4)\n");
}

#size scalar altivec altivec-ng libmoto
13 6 1 5 5
test1 = test3)
test1 = test4)
test3 = test4)
16 7 1 5 6
test1 = test2)
test1 = test3)
test1 = test4)
test2 = test3)
test2 = test4)
test3 = test4)
27 11 2 4 4
test1 = test3)
test1 = test4)
test3 = test4)
64 27 2 5 4
test1 = test2)
test1 = test4)
test2 = test4)
90 37 3 6 4
test1 = test4)
128 58 4 7 6
test1 = test2)
test1 = test4)
test2 = test4)
185 75 6 7 8
test1 = test4)
256 106 7 9 7
test1 = test2)
test1 = test4)
test2 = test4)
347 141 10 10 10
test1 = test4)
512 208 14 13 11
test1 = test2)
test1 = test4)
test2 = test4)
831 338 21 20 15
test1 = test4)
2048 832 53 43 30
test1 = test2)
test1 = test4)
test2 = test4)
3981 1617 102 79 55
test1 = test4)
8192 3329 208 161 108
test1 = test2)
test1 = test4)
test2 = test4)

// now store a number of aligned vectors
  while (len >= 64) {
    vec_st(fillchar, 0, ptrfirst);
    len -= 64;
    vec_st(fillchar, 16, ptrfirst);
    vec_st(fillchar, 32, ptrfirst);
    vec_st(fillchar, 48, ptrfirst);
    ptrfirst += 64;
  }

  if (len >= 32) {
    vec_st(fillchar, 0, ptrfirst);
    len -= 32;
    vec_st(fillchar, 16, ptrfirst);
    ptrfirst += 32;
  }

  if (len >= 16) {
    vec_st(fillchar, 0, ptrfirst);
    ptrfirst += 16;
    len -= 16;
  }

unsigned char *vec_strfill(unsigned char *s, int len, char p) {
assert(len > 0); // sanity check

// build a vector full of copies of p
vector unsigned char fillchar = vec_splat(vec_lvsl(0,(unsigned char*)&p), 0);
fillchar = vec_perm(vec_ld(0, (unsigned char*)&p), fillchar, fillchar);

vector unsigned char firstmask, lastmask;

{ // local scope limits lifetime of temporary variables
vector unsigned char ones, zeros; // to build constant values
ones = (vector unsigned char) vec_cmpeq(fillchar, fillchar); // 0xff
zeros = (vector unsigned char) vec_sub(fillchar, fillchar); // 0x00
// the instructions chosen here go to the VSIU and can potentially be
// executed in parallel with a pair going to VPU and LSU

firstmask = vec_perm(zeros, ones, vec_lvsr(0, s));
// lastmask will be zero when the string's end is aligned
lastmask = vec_perm(ones, zeros, vec_lvsr(len, s));
}

// check if firstmask and lastmask have to be combined
if (len <= (((int)s & 15) ^ 15)) {
vec_st(vec_sel(vec_ld(0,s), fillchar, vec_and(firstmask, lastmask)), 0,s);
return s;
}

// check if a last partial vector needs to be handled
if (vec_all_eq(vec_splat_u8(0), lastmask)) {
// no, string ends with aligned vector, so just do first partial vector
vec_st(vec_sel(vec_ld(0, s), fillchar, firstmask), 0, s);
} else {
// do both partial vectors in parallel for better pipeline utilization
vector unsigned char firstdata = vec_ld(0, s);
vector unsigned char lastdata = vec_ld(len, s);
firstdata = vec_sel(firstdata, fillchar, firstmask);
lastdata = vec_sel(lastdata, fillchar, lastmask);
vec_st(firstdata, 0, s);
vec_st(lastdata, len, s);
}

// handle remaining aligned vectors
len -= 1; // number of chars handled in first vector
len -= ((int)s & 15 ^ 15);
len &= ~15; // number of chars handled in last vector

// when there are many short strings, it might pay to do an early exit here
if (len == 0) return s;

unsigned char* cursor = s + 16; // skip first vector (already processed)

// now store a number of aligned vectors
while (len >= 64) {
vec_st(fillchar, 0, cursor);
len -= 64;
vec_st(fillchar, 16, cursor);
vec_st(fillchar, 32, cursor);
vec_st(fillchar, 48, cursor);
cursor += 64;
}

if (len >= 32) {
vec_st(fillchar, 0, cursor);
len -= 32;
vec_st(fillchar, 16, cursor);
cursor += 32;
}

if (len > 0) {
vec_st(fillchar, 0, cursor);
cursor += 16;
len -= 16;
}

assert(len == 0); // sanity check

return s;
}