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IMPORT: ebtree: implement and use flsnz_long() to count bits

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The asm code shows multiple conversions. Gcc has always been terribly
bad at dealing with chars, which are constantly converted to ints for
every operation and zero-extended after each operation. But here in
addition there are conversions before and after the flsnz(). Let's
just mark the variables as long and use flsnz_long() to process them
without any conversion. This shortens the code and makes it slightly
faster.

Note that the fls operations could make use of __builtin_clz() on
gcc 4.6 and above, and it would be useful to implement native support
for ARM as well.

This is cbtree commit 1f0f83ba26f2279c8bba0080a2e09a803dddde47.
This is ebtree commit 9c38dcae22a84f0b0d9c5a56facce1ca2ad0aaef.
This commit is contained in:
Willy Tarreau 2023-12-17 16:43:25 +01:00
parent 57f8a4e879
commit 9afe3b59a7
1 changed files with 11 additions and 4 deletions
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15
include/import/ebtree.h
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@ -279,6 +279,14 @@ static inline int flsnz8(unsigned char x)
return r+1;
}
static inline long flsnz_long(unsigned long x)
{
long r;
__asm__("bsr %1,%0\n"
: "=r" (r) : "rm" (x));
return r + 1;
}
#else
// returns 1 to 32 for 1<<0 to 1<<31. Undefined for 0.
#define flsnz(___a) ({ \
@ -297,6 +305,7 @@ static inline int flsnz8(unsigned int x)
return flsnz8_generic(x);
}
#define flsnz_long(x) ((sizeof(long) > 4) ? flsnz64(x) : flsnz32(x))
#endif
@ -791,7 +800,7 @@ static forceinline int string_equal_bits(const unsigned char *a,
int ignore)
{
int beg;
unsigned char c;
unsigned long c, d;
beg = ignore >> 3;
@ -799,8 +808,6 @@ static forceinline int string_equal_bits(const unsigned char *a,
* or at the first zero we encounter on either side.
*/
while (1) {
unsigned char d;
c = a[beg];
d = b[beg];
beg++;
@ -816,7 +823,7 @@ static forceinline int string_equal_bits(const unsigned char *a,
* identical bits. Note that low bit numbers are assigned to high positions
* in the byte, as we compare them as strings.
*/
return (beg << 3) - flsnz8(c);
return (beg << 3) - flsnz_long(c);
}
static forceinline int cmp_bits(const unsigned char *a, const unsigned char *b, unsigned int pos)