basic/bitfield: add bitfield operations

Add macros to manage bits in a bitfield (e.g. uint32_t, uint64_t, etc),
such as setting, clearing, checking bits, and iterating all set bits.

These are similiar to the bitmap operations, but operate on basic types
instead of requiring a Bitmap object.

(cherry picked from commit 33d9bee)

src/basic/bitfield.h

@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "macro.h"
+
+/* Bit index (0-based) to mask of specified type. Assertion failure if index is out of range. */
+#define _INDEX_TO_MASK(type, i, uniq)                                   \
+        ({                                                              \
+                int UNIQ_T(_i, uniq) = (i);                             \
+                assert(UNIQ_T(_i, uniq) < (int)sizeof(type) * 8);       \
+                ((type)1) << UNIQ_T(_i, uniq);                          \
+        })
+#define INDEX_TO_MASK(type, i)                                          \
+        ({                                                              \
+                assert_cc(sizeof(type) <= sizeof(unsigned long long));  \
+                assert_cc(__builtin_choose_expr(__builtin_constant_p(i), i, 0) < (int)(sizeof(type) * 8)); \
+                __builtin_choose_expr(__builtin_constant_p(i),          \
+                                      ((type)1) << (i),                 \
+                                      _INDEX_TO_MASK(type, i, UNIQ));   \
+        })
+
+/* Builds a mask of specified type with multiple bits set. Note the result will not be constant, even if all
+ * indexes are constant. */
+#define INDEXES_TO_MASK(type, ...)                              \
+        UNIQ_INDEXES_TO_MASK(type, UNIQ, ##__VA_ARGS__)
+#define UNIQ_INDEXES_TO_MASK(type, uniq, ...)                           \
+        ({                                                              \
+                typeof(type) UNIQ_T(_mask, uniq) = (type)0;             \
+                int UNIQ_T(_i, uniq);                                   \
+                VA_ARGS_FOREACH(UNIQ_T(_i, uniq), ##__VA_ARGS__)        \
+                        UNIQ_T(_mask, uniq) |= INDEX_TO_MASK(type, UNIQ_T(_i, uniq)); \
+                UNIQ_T(_mask, uniq);                                    \
+        })
+
+/* Same as the FLAG macros, but accept a 0-based bit index instead of a mask. Results in assertion failure if
+ * index is out of range for the type. */
+#define SET_BIT(bits, i) SET_FLAG(bits, INDEX_TO_MASK(typeof(bits), i), true)
+#define CLEAR_BIT(bits, i) SET_FLAG(bits, INDEX_TO_MASK(typeof(bits), i), false)
+#define BIT_SET(bits, i) FLAGS_SET(bits, INDEX_TO_MASK(typeof(bits), i))
+
+/* As above, but accepts multiple indexes. Note the result will not be constant, even if all indexes are
+ * constant. */
+#define SET_BITS(bits, ...) SET_FLAG(bits, INDEXES_TO_MASK(typeof(bits), ##__VA_ARGS__), true)
+#define CLEAR_BITS(bits, ...) SET_FLAG(bits, INDEXES_TO_MASK(typeof(bits), ##__VA_ARGS__), false)
+#define BITS_SET(bits, ...) FLAGS_SET(bits, INDEXES_TO_MASK(typeof(bits), ##__VA_ARGS__))
+
+/* Iterate through each set bit. Index is 0-based and type int. */
+#define BIT_FOREACH(index, bits) _BIT_FOREACH(index, bits, UNIQ)
+#define _BIT_FOREACH(index, bits, uniq)                                 \
+        for (int UNIQ_T(_last, uniq) = -1, index;                       \
+             (index = BIT_NEXT_SET(bits, UNIQ_T(_last, uniq))) >= 0;    \
+             UNIQ_T(_last, uniq) = index)
+
+/* Find the next set bit after 0-based index 'prev'. Result is 0-based index of next set bit, or -1 if no
+ * more bits are set. */
+#define BIT_FIRST_SET(bits) BIT_NEXT_SET(bits, -1)
+#define BIT_NEXT_SET(bits, prev)                        \
+        UNIQ_BIT_NEXT_SET(bits, prev, UNIQ)
+#define UNIQ_BIT_NEXT_SET(bits, prev, uniq)                             \
+        ({                                                              \
+                typeof(bits) UNIQ_T(_bits, uniq) = (bits);              \
+                int UNIQ_T(_prev, uniq) = (prev);                       \
+                int UNIQ_T(_next, uniq);                                \
+                _BIT_NEXT_SET(UNIQ_T(_bits, uniq),                      \
+                              UNIQ_T(_prev, uniq),                      \
+                              UNIQ_T(_next, uniq));                     \
+        })
+#define _BIT_NEXT_SET(bits, prev, next)                                 \
+        ((int)(prev + 1) == (int)sizeof(bits) * 8                       \
+         ? -1 /* Prev index was msb. */                                 \
+         : ((next = __builtin_ffsll(((unsigned long long)(bits)) >> (prev + 1))) == 0 \
+            ? -1 /* No more bits set. */                                \
+            : prev + next))