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Optimize string repetition and string copying #2634

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Merged
merged 6 commits into from
Apr 4, 2024
Merged

Optimize string repetition and string copying #2634

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81b4810
Faster string repeat algorithm
advikkabra Mar 28, 2024
d76d2ea
Optimize `_lfortran_strcpy`
advikkabra Mar 28, 2024
7d2080c
Faster string repeat algorithm
advikkabra Mar 28, 2024
d6645f5
Optimize `_lfortran_strcpy`
advikkabra Mar 28, 2024
130ca48
Added stress test for repeat
advikkabra Apr 3, 2024
12622b1
Merge branch 'optimize-repeat' of https://github.com/advikkabra/lpyth…
advikkabra Apr 3, 2024
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1 change: 1 addition & 0 deletions integration_tests/test_str_01.py
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,7 @@ def test_str_repeat():
assert a*2*3 == "XyzXyzXyzXyzXyzXyz"
assert 3*a*3 == "XyzXyzXyzXyzXyzXyzXyzXyzXyz"
assert a*-1 == ""
assert len(a*(10**6)) == (3 * 10 ** 6)

def test_str_join():
a: str
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34 changes: 22 additions & 12 deletions src/libasr/runtime/lfortran_intrinsics.c
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Expand Up @@ -1976,12 +1976,14 @@ LFORTRAN_API void _lfortran_strcpy(char** x, char *y, int8_t free_target)
*x = (char*) malloc((strlen(y) + 1) * sizeof(char));
_lfortran_string_init(strlen(y) + 1, *x);
// }
for (size_t i = 0; i < strlen(*x); i++) {
if (i < strlen(y)) {
x[0][i] = y[i];
} else {
x[0][i] = ' ';
}
size_t y_len = strlen(y);
size_t x_len = strlen(*x);
size_t i = 0;
for (; i < x_len && i < y_len; i++) {
x[0][i] = y[i];
}
for (; i < x_len; i++) {
x[0][i] = ' ';
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This is a great improvement. Thanks!

}
}

Expand Down Expand Up @@ -2129,21 +2131,29 @@ LFORTRAN_API int32_t _lpython_bit_length8(int64_t num)
//repeat str for n time
LFORTRAN_API void _lfortran_strrepeat(char** s, int32_t n, char** dest)
{
int cntr = 0;
char trmn = '\0';
int s_len = strlen(*s);
int trmn_size = sizeof(trmn);
int f_len = s_len*n;
if (f_len < 0)
f_len = 0;
char* dest_char = (char*)malloc(f_len+trmn_size);
for (int i = 0; i < n; i++) {
for (int j = 0; j < s_len; j++) {
dest_char[cntr] = (*s)[j];
cntr++;

if (s_len == 1) {
memset(dest_char, *(*s), n);
} else {
Comment on lines +2142 to +2144
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I wonder why we need to handle the case for s_len == 1 separately. The else portion seems general, so I think that should be enough to handle the case of s_len == 1.

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Does the else portion fail when s_len == 1?

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@advikkabra advikkabra Mar 29, 2024 •
edited
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It does not fail when s_len == 1, but memset is very optimized for this usecase. Setting a large block of data to a single value is what memset excels in, and it is optimized for every architecture. While testing, these are the compared times:

100000000
Binary exponentiation: 0.086963
memset: 0.006341

400000000
Binary exponentiation: 0.211737
memset: 0.018612

This is after compiling with -O3

memcpy(dest_char, *s, s_len);
int chars_copied = s_len;
int copy_length;
while (chars_copied < f_len) {
copy_length = (chars_copied <= f_len-chars_copied)
? chars_copied : f_len-chars_copied;
memcpy(dest_char+chars_copied, dest_char, copy_length);
chars_copied += copy_length;
}
}
dest_char[cntr] = trmn;

dest_char[f_len] = trmn;
*dest = &(dest_char[0]);
}

Expand Down