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https://gitlab.gnome.org/GNOME/glib.git
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dce88768dc
We should have done this a decade ago... https://bugzilla.gnome.org/show_bug.cgi?id=730293
146 lines
2.8 KiB
C
146 lines
2.8 KiB
C
#include <glib.h>
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#if defined(__GNUC__) && (__GNUC__ >= 4)
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# define TEST_BUILTINS 1
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#else
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# define TEST_BUILTINS 0
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#endif
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#if TEST_BUILTINS
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static gint
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builtin_bit_nth_lsf1 (gulong mask, gint nth_bit)
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{
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if (nth_bit >= 0)
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{
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if (G_LIKELY (nth_bit < GLIB_SIZEOF_LONG * 8 - 1))
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mask &= -(1UL<<(nth_bit+1));
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else
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mask = 0;
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}
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return __builtin_ffsl(mask) - 1;
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}
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static gint
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builtin_bit_nth_lsf2 (gulong mask, gint nth_bit)
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{
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if (nth_bit >= 0)
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{
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if (G_LIKELY (nth_bit < GLIB_SIZEOF_LONG * 8 - 1))
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mask &= -(1UL<<(nth_bit+1));
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else
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mask = 0;
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}
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return mask ? __builtin_ctzl(mask) : -1;
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}
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static gint
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builtin_bit_nth_msf (gulong mask, gint nth_bit)
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{
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if (nth_bit >= 0 && nth_bit < GLIB_SIZEOF_LONG * 8)
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mask &= (1UL<<nth_bit)-1;
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return mask ? GLIB_SIZEOF_LONG * 8 - 1 - __builtin_clzl(mask) : -1;
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}
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static guint
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builtin_bit_storage (gulong number)
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{
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return number ? GLIB_SIZEOF_LONG * 8 - __builtin_clzl(number) : 1;
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}
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#endif
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static gint
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naive_bit_nth_lsf (gulong mask, gint nth_bit)
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{
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if (G_UNLIKELY (nth_bit < -1))
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nth_bit = -1;
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while (nth_bit < ((GLIB_SIZEOF_LONG * 8) - 1))
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{
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nth_bit++;
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if (mask & (1UL << nth_bit))
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return nth_bit;
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}
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return -1;
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}
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static gint
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naive_bit_nth_msf (gulong mask, gint nth_bit)
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{
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if (nth_bit < 0 || G_UNLIKELY (nth_bit > GLIB_SIZEOF_LONG * 8))
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nth_bit = GLIB_SIZEOF_LONG * 8;
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while (nth_bit > 0)
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{
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nth_bit--;
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if (mask & (1UL << nth_bit))
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return nth_bit;
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}
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return -1;
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}
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static guint
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naive_bit_storage (gulong number)
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{
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guint n_bits = 0;
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do
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{
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n_bits++;
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number >>= 1;
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}
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while (number);
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return n_bits;
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}
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#define TEST(f1, f2, i) \
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if (f1 (i) != f2 (i)) { \
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g_error (G_STRINGIFY (f1) " (%lu) = %d; " \
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G_STRINGIFY (f2) " (%lu) = %d; ", \
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i, f1 (i), \
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i, f2 (i)); \
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return 1; \
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}
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#define TEST2(f1, f2, i, n) \
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if (f1 (i, n) != f2 (i, n)) { \
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g_error (G_STRINGIFY (f1) " (%lu, %d) = %d; " \
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G_STRINGIFY (f2) " (%lu, %d) = %d; ", \
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i, n, f1 (i, n), \
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i, n, f2 (i, n)); \
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return 1; \
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}
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int
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main (void)
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{
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gulong i;
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gint nth_bit;
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/* we loop like this: 0, -1, 1, -2, 2, -3, 3, ... */
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for (i = 0; (glong)i < 1500 ; i = -(i+((glong)i>=0))) {
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#if TEST_BUILTINS
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TEST (naive_bit_storage, builtin_bit_storage, i);
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#endif
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TEST (naive_bit_storage, g_bit_storage, i);
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for (nth_bit = -3; nth_bit <= 2 + GLIB_SIZEOF_LONG * 8; nth_bit++) {
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#if TEST_BUILTINS
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TEST2 (naive_bit_nth_lsf, builtin_bit_nth_lsf1, i, nth_bit);
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TEST2 (naive_bit_nth_lsf, builtin_bit_nth_lsf2, i, nth_bit);
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#endif
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TEST2 (naive_bit_nth_lsf, g_bit_nth_lsf, i, nth_bit);
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#if TEST_BUILTINS
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TEST2 (naive_bit_nth_msf, builtin_bit_nth_msf, i, nth_bit);
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#endif
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TEST2 (naive_bit_nth_msf, g_bit_nth_msf, i, nth_bit);
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}
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}
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return 0;
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}
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