git: 605389e40b93 - stable/15 - sys/bitcount.h: add __const_bitcount<n>

The branch stable/15 has been updated by bz:

URL: https://cgit.FreeBSD.org/src/commit/?id=605389e40b938088718bd8aa75f4919884789927

commit 605389e40b938088718bd8aa75f4919884789927
Author:     Bjoern A. Zeeb <bz@FreeBSD.org>
AuthorDate: 2025-09-15 23:54:57 +0000
Commit:     Bjoern A. Zeeb <bz@FreeBSD.org>
CommitDate: 2026-01-16 08:48:47 +0000

    sys/bitcount.h: add __const_bitcount<n>
    
    Add a version of __const_bitcount<n> which can be used to get the
    numbers at compile-time when __builtin_popcountg() is not available
    (see sys/compat/linuxkpi/common/include/linux/bitops.h for LLVM before
    19 and gcc before 14).
    
    Obtained from:  https://reviews.freebsd.org/D50995#1174884 by obiwac
    Sponsored by:   The FreeBSD Foundation
    Reviewed by:    brooks, emaste
    Differential Revision: https://reviews.freebsd.org/D54301
    
    (cherry picked from commit 27aa23cee81088b0ffa974eec9f03c654c36438e)
---
 sys/sys/bitcount.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/sys/sys/bitcount.h b/sys/sys/bitcount.h
index 171425032680..919dc4be06fc 100644
--- a/sys/sys/bitcount.h
+++ b/sys/sys/bitcount.h
@@ -39,6 +39,28 @@
 
 #include <sys/_types.h>
 
+#define	__const_bitcount8(x) ( \
+    !!((x) & (1 << 0)) + \
+    !!((x) & (1 << 1)) + \
+    !!((x) & (1 << 2)) + \
+    !!((x) & (1 << 3)) + \
+    !!((x) & (1 << 4)) + \
+    !!((x) & (1 << 5)) + \
+    !!((x) & (1 << 6)) + \
+    !!((x) & (1 << 7)))
+
+#define	__const_bitcount16(x) ( \
+    __const_bitcount8(x) + \
+    __const_bitcount8((x) >> 8))
+
+#define	__const_bitcount32(x) ( \
+    __const_bitcount16(x) + \
+    __const_bitcount16((x) >> 16))
+
+#define	__const_bitcount64(x) ( \
+    __const_bitcount32(x) + \
+    __const_bitcount32((x) >> 32))
+
 #ifdef __POPCNT__
 #define	__bitcount64(x)	__builtin_popcountll((__uint64_t)(x))
 #define	__bitcount32(x)	__builtin_popcount((__uint32_t)(x))