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00a31dd3ac
linux/include/asm-generic
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Nicolas Pitre 00a31dd3ac
asm-generic/div64: optimize/simplify __div64_const32() 
Several years later I just realized that this code could be greatly
simplified.

First, let's formalize the need for overflow handling in
__arch_xprod64(). Assuming n = UINT64_MAX, there are 2 cases where
an overflow may occur:

1) If a bias must be added, we have m_lo * n_lo + m or
   m_lo * 0xffffffff + ((m_hi << 32) + m_lo) or
   ((m_lo << 32) - m_lo) + ((m_hi << 32) + m_lo) or
   (m_lo + m_hi) << 32 which must be < (1 << 64). So the criteria for no
   overflow is m_lo + m_hi < (1 << 32).

2) The cross product m_lo * n_hi + m_hi * n_lo or
   m_lo * 0xffffffff + m_hi * 0xffffffff or
   ((m_lo << 32) - m_lo) + ((m_hi << 32) - m_hi). Assuming the top
   result from the previous step (m_lo + m_hi) that must be added to
   this, we get (m_lo + m_hi) << 32 again.

So let's have a straight and simpler version when this is true.
Otherwise some reordering allows for taking care of possible overflows
without any actual conditionals. And prevent from generating both code
variants by making sure this is considered only if m is perceived as
constant by the compiler.

This, in turn, allows for greatly simplifying __div64_const32(). The
"special case" may go as well as the regular case works just fine
without needing a bias. Then reduction should be applied all the time as
minimizing m is the key.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
2024-10-28 21:44:28 +00:00
..
bitops bitops: Change function return types from long to int 2024-05-03 17:04:50 +02:00
vdso lib/vdso: Avoid highres update if clocksource is not VDSO capable 2020-02-17 20:12:17 +01:00
access_ok.h uaccess: remove CONFIG_SET_FS 2022-02-25 09:36:06 +01:00
agp.h char/agp: introduce asm-generic/agp.h 2023-02-13 22:13:29 +01:00
archrandom.h random: handle archrandom with multiple longs 2022-07-25 13:26:14 +02:00
asm-offsets.h asm-generic: Add common asm-offsets.h 2015-06-23 13:35:49 +09:00
asm-prototypes.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
atomic64.h locking/atomic: delete !ARCH_ATOMIC remnants 2021-05-26 13:20:52 +02:00
atomic.h locking/atomic: make atomic*_{cmp,}xchg optional 2023-06-05 09:57:14 +02:00
audit_change_attr.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
audit_dir_write.h audit: Avoid build failures on systems without renameat 2018-01-30 19:07:54 -08:00
audit_read.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
audit_signal.h
audit_write.h audit/stable-4.15 PR 20171113 2017-11-15 13:28:48 -08:00
barrier.h sched: Add missing memory barrier in switch_mm_cid 2024-04-16 13:59:45 +02:00
bitops.h include: move find.h from asm_generic to linux 2022-01-15 08:47:31 -08:00
bitsperlong.h lib: extend the scope of small_const_nbits() macro 2021-05-06 19:24:11 -07:00
bug.h bug: Improve comment 2024-05-07 14:20:48 +02:00
cache.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
cacheflush.h mm: Introduce flush_cache_vmap_early() 2023-12-14 00:23:17 -08:00
cfi.h cfi: Flip headers 2023-12-15 16:25:55 -08:00
checksum.h asm-generic: Improve csum_fold 2024-01-17 17:52:29 -08:00
cmpxchg-local.h asm-generic: Fix 32 bit __generic_cmpxchg_local 2024-01-05 23:19:14 +01:00
cmpxchg.h asm-generic: avoid __generic_cmpxchg_local warnings 2023-04-04 17:58:11 +02:00
codetag.lds.h lib: add allocation tagging support for memory allocation profiling 2024-04-25 20:55:52 -07:00
compat.h asm-generic: compat: fix compat_arg_u64() and compat_arg_u64_dual() 2022-11-01 10:20:11 +11:00
current.h asm-generic: current: Don't include thread-info.h if building asm 2023-08-26 22:38:49 +02:00
delay.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
device.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 428 2019-06-05 17:37:16 +02:00
div64.h asm-generic/div64: optimize/simplify __div64_const32() 2024-10-28 21:44:28 +00:00
dma-mapping.h dma-mapping: no need to pass a bus_type into get_arch_dma_ops() 2023-02-15 12:35:20 +01:00
dma.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
early_ioremap.h mm/early_ioremap.c: remove redundant early_ioremap_shutdown() 2021-09-08 11:50:24 -07:00
emergency-restart.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
error-injection.h docs: fault-injection: add requirements of error injectable functions 2023-02-02 22:50:00 -08:00
exec.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
extable.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fixmap.h fixmap: Remove unused set_fixmap_offset_io() 2024-07-11 17:41:23 +02:00
flat.h binfmt_flat: remove the persistent argument from flat_get_addr_from_rp 2019-06-24 09:16:47 +10:00
ftrace.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
futex.h futex: Fix additional regressions 2021-12-11 23:31:51 +01:00
getorder.h asm-generic: force inlining of get_order() to work around gcc10 poor decision 2020-12-15 22:46:15 -08:00
hardirq.h irqstat: Move declaration into asm-generic/hardirq.h 2020-11-23 10:31:06 +01:00
hugetlb.h mm: provide mm_struct and address to huge_ptep_get() 2024-07-12 15:52:15 -07:00
hw_irq.h
hyperv-tlfs.h hyperv-fixes for v6.9-rc4 2024-04-11 16:23:56 -07:00
int-ll64.h int-ll64.h: define u{8,16,32,64} and s{8,16,32,64} based on uapi header 2018-06-07 17:34:38 -07:00
io.h asm-generic/io.h: Remove I/O port accessors for HAS_IOPORT=n 2024-10-28 21:44:28 +00:00
ioctl.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
iomap.h asm-generic/iomap.h: remove ARCH_HAS_IOREMAP_xx macros 2023-08-18 10:12:32 -07:00
irq_regs.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
irq_work.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
irq.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
irqflags.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kbuild move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
kdebug.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kmap_size.h mm/highmem: Provide and use CONFIG_DEBUG_KMAP_LOCAL 2020-11-24 14:42:08 +01:00
kprobes.h treewide: Convert macro and uses of __section(foo) to __section("foo") 2020-10-25 14:51:49 -07:00
kvm_para.h KVM: Introduce paravirtualization hints and KVM_HINTS_DEDICATED 2018-03-06 18:40:44 +01:00
kvm_types.h KVM: Move x86's version of struct kvm_mmu_memory_cache to common code 2020-07-09 13:29:42 -04:00
linkage.h
local64.h locking/generic: Wire up local{,64}_try_cmpxchg() 2023-04-29 09:09:09 +02:00
local.h locking/generic: Wire up local{,64}_try_cmpxchg() 2023-04-29 09:09:09 +02:00
logic_io.h logic_io instance of iounmap() needs volatile on argument 2021-12-21 21:31:08 +01:00
mcs_spinlock.h locking/mcs: Allow architecture specific asm files to be used for contended case 2014-02-09 21:18:52 +01:00
memory_model.h asm-generic: add an optional pfn_valid check to page_to_phys 2024-10-28 21:44:28 +00:00
mm_hooks.h mm: remove arch_unmap() 2024-09-01 20:26:13 -07:00
mmiowb_types.h asm-generic/mmiowb: Add generic implementation of mmiowb() tracking 2019-04-08 11:59:39 +01:00
mmiowb.h asm-generic/mmiowb: Allow mmiowb_set_pending() when preemptible() 2020-07-17 10:02:03 +01:00
mmu_context.h asm-generic: add generic MMU versions of mmu context functions 2020-10-26 16:45:03 +01:00
mmu.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mmzone.h arch, mm: move definition of node_data to generic code 2024-09-03 21:15:28 -07:00
module.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
module.lds.h kbuild: preprocess module linker script 2020-09-25 00:36:41 +09:00
mshyperv.h hyperv-fixes for v6.9-rc4 2024-04-11 16:23:56 -07:00
msi.h genirq: Get rid of GENERIC_MSI_IRQ_DOMAIN 2022-11-17 15:15:20 +01:00
nommu_context.h asm-generic: add generic MMU versions of mmu context functions 2020-10-26 16:45:03 +01:00
numa.h arch_numa: switch over to numa_memblks 2024-09-03 21:15:32 -07:00
param.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
parport.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pci_iomap.h PCI: Stub __pci_ioport_map() for arches that don't support it at all 2022-07-29 12:01:00 -05:00
pci.h asm-generic: Add new pci.h and use it 2022-07-22 17:34:57 -05:00
percpu.h percpu: Fix self-assignment of __old in raw_cpu_generic_try_cmpxchg() 2023-06-08 10:28:39 +02:00
pgalloc.h mm: change inlined allocation helpers to account at the call site 2024-04-25 20:55:59 -07:00
pgtable_uffd.h userfaultfd: wp: add pmd_swp_*uffd_wp() helpers 2020-04-07 10:43:39 -07:00
pgtable-nop4d.h mm: rename p4d_page_vaddr to p4d_pgtable and make it return pud_t * 2021-07-08 11:48:22 -07:00
pgtable-nopmd.h mm: recover pud_leaf() definitions in nopmd case 2024-03-13 12:12:21 -07:00
pgtable-nopud.h mm: rename p4d_page_vaddr to p4d_pgtable and make it return pud_t * 2021-07-08 11:48:22 -07:00
preempt.h riscv: support PREEMPT_DYNAMIC with static keys 2023-08-31 00:18:34 -07:00
qrwlock_types.h locking/qrwlock: Change "queue rwlock" to "queued rwlock" 2022-05-11 16:27:04 +02:00
qrwlock.h asm-generic changes for 5.19 2022-05-26 10:50:30 -07:00
qspinlock_types.h locking/qspinlock: Do not include atomic.h from qspinlock_types.h 2020-07-29 16:14:19 +02:00
qspinlock.h asm-generic: qspinlock: fix queued_spin_value_unlocked() implementation 2023-11-22 09:32:49 -08:00
resource.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
runtime-const.h runtime constants: add default dummy infrastructure 2024-06-19 12:34:34 -07:00
rwonce.h asm/rwonce: Don't pull <asm/barrier.h> into 'asm-generic/rwonce.h' 2020-07-21 10:50:36 +01:00
seccomp.h seccomp: Use -1 marker for end of mode 1 syscall list 2020-07-10 16:01:52 -07:00
sections.h jump_label,module: Don't alloc static_key_mod for __ro_after_init keys 2024-03-22 11:18:16 +01:00
serial.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
set_memory.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
shmparam.h treewide: remove SPDX "WITH Linux-syscall-note" from kernel-space headers 2019-05-14 19:52:48 -07:00
signal.h asm-generic: Remove empty #ifdef SA_RESTORER 2022-09-10 09:56:53 +02:00
simd.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
softirq_stack.h asm-generic: Conditionally enable do_softirq_own_stack() via Kconfig. 2022-09-05 17:20:55 +02:00
spinlock_types.h asm-generic: ticket-lock: New generic ticket-based spinlock 2022-05-11 11:49:38 -07:00
spinlock.h asm-generic: ticket-lock: Optimize arch_spin_value_unlocked() 2023-09-21 10:17:00 +02:00
statfs.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
string.h
switch_to.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
syscall.h ptrace: Create ptrace_report_syscall_{entry,exit} in ptrace.h 2022-03-10 13:35:08 -06:00
syscalls.h syscalls: mmap(): use unsigned offset type consistently 2024-06-25 15:57:38 +02:00
timex.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
tlb.h mm/mmu_gather: add __tlb_remove_folio_pages() 2024-02-22 15:27:17 -08:00
tlbflush.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
topology.h mm: replace CONFIG_NEED_MULTIPLE_NODES with CONFIG_NUMA 2021-06-29 10:53:55 -07:00
trace_clock.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
uaccess.h move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
user.h
vermagic.h arch: split MODULE_ARCH_VERMAGIC definitions out to <asm/vermagic.h> 2020-04-23 10:50:26 +09:00
vga.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
video.h arch: Rename fbdev header and source files 2024-05-03 17:07:50 +02:00
vmlinux.lds.h asm-generic updates for 6.12 2024-09-26 11:54:40 -07:00
word-at-a-time.h kernel.h: removed REPEAT_BYTE from kernel.h 2024-02-01 09:47:59 -08:00
xor.h lib/xor: make xor prototypes more friendly to compiler vectorization 2022-02-11 20:39:39 +11:00