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seq: omit unnecessary malloc for upper bound

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* src/seq.c (seq_fast): Speed up test for "inf".
Do not allocate and free a copy of B, as it is fine as-is.
This commit is contained in:
Paul Eggert
2024-11-08 12:28:27 -08:00
parent 59bfd5b53d
commit 96e101d03f
1 changed files with 5 additions and 16 deletions
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21
src/seq.c
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@@ -457,37 +457,27 @@ trim_leading_zeros (char const *s)
static void
seq_fast (char const *a, char const *b, uintmax_t step)
{
bool inf = STREQ (b, "inf");
/* Skip past any redundant leading '0's. Without this, our naive cmp
function would declare 000 to be larger than 99. */
a = trim_leading_zeros (a);
b = trim_leading_zeros (b);
idx_t p_len = strlen (a);
idx_t q_len = inf ? 0 : strlen (b);
idx_t b_len = strlen (b);
bool inf = b_len == 3 && memcmp (b, "inf", 4) == 0;
/* Allow for at least 31 digits without realloc.
1 more than p_len is needed for the inf case. */
enum { INITIAL_ALLOC_DIGITS = 31 };
idx_t inc_size = MAX (MAX (p_len + 1, q_len), INITIAL_ALLOC_DIGITS);
idx_t inc_size = MAX (MAX (p_len + 1, b_len), INITIAL_ALLOC_DIGITS);
/* Ensure we only increase by at most 1 digit at buffer boundaries. */
static_assert (SEQ_FAST_STEP_LIMIT_DIGITS < INITIAL_ALLOC_DIGITS - 1);
/* Copy input strings (incl NUL) to end of new buffers. */
char *p0 = xmalloc (inc_size + 1);
char *p = memcpy (p0 + inc_size - p_len, a, p_len + 1);
char *q;
char *q0;
if (! inf)
{
q0 = xmalloc (inc_size + 1);
q = memcpy (q0 + inc_size - q_len, b, q_len + 1);
}
else
q = q0 = nullptr;
bool ok = inf || cmp (p, p_len, q, q_len) <= 0;
bool ok = inf || cmp (p, p_len, b, b_len) <= 0;
if (ok)
{
/* Reduce number of fwrite calls which is seen to
@@ -510,7 +500,7 @@ seq_fast (char const *a, char const *b, uintmax_t step)
p -= incr_grows (p, endp);
p_len = endp - p;
if (! inf && 0 < cmp (p, p_len, q, q_len))
if (! inf && 0 < cmp (p, p_len, b, b_len))
break;
*bufp++ = *separator;
@@ -553,7 +543,6 @@ seq_fast (char const *a, char const *b, uintmax_t step)
exit (EXIT_SUCCESS);
free (p0);
free (q0);
}
/* Return true if S consists of at least one digit and no non-digits. */