| Message ID | 20250409154356.423512-2-visitorckw@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Introduce parity_odd() and refactor redundant parity code | expand |
On Wed, Apr 09, 2025 at 11:43:44PM +0800, Kuan-Wei Chiu wrote: > Redesign the parity8() helper as parity_odd(), changing its input type > from u8 to u64 to support broader use cases and its return type from > int to bool to clearly reflect the function's binary output. The > function now returns true for odd parity and false for even parity, > making its behavior more intuitive based on the name. > > Also mark the function with __attribute_const__ to enable better > compiler optimization, as the result depends solely on its input and > has no side effects. > > While more efficient implementations may exist, further optimization is > postponed until a use case in performance-critical paths arises. > > Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com> > Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com> > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com> > --- > arch/x86/kernel/bootflag.c | 4 ++-- > drivers/hwmon/spd5118.c | 2 +- > drivers/i3c/master/dw-i3c-master.c | 2 +- > drivers/i3c/master/i3c-master-cdns.c | 2 +- > drivers/i3c/master/mipi-i3c-hci/dat_v1.c | 2 +- > include/linux/bitops.h | 19 ++++++++++++------- > 6 files changed, 18 insertions(+), 13 deletions(-) > > diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c > index 73274d76ce16..86aae4b2bfd5 100644 > --- a/arch/x86/kernel/bootflag.c > +++ b/arch/x86/kernel/bootflag.c > @@ -26,7 +26,7 @@ static void __init sbf_write(u8 v) > unsigned long flags; > > if (sbf_port != -1) { > - if (!parity8(v)) > + if (!parity_odd(v)) > v ^= SBF_PARITY; > > printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n", > @@ -57,7 +57,7 @@ static bool __init sbf_value_valid(u8 v) > { > if (v & SBF_RESERVED) /* Reserved bits */ > return false; > - if (!parity8(v)) > + if (!parity_odd(v)) > return false; > > return true; > diff --git a/drivers/hwmon/spd5118.c b/drivers/hwmon/spd5118.c > index 358152868d96..15761f2ca4e9 100644 > --- a/drivers/hwmon/spd5118.c > +++ b/drivers/hwmon/spd5118.c > @@ -298,7 +298,7 @@ static umode_t spd5118_is_visible(const void *_data, enum hwmon_sensor_types typ > */ > static bool spd5118_vendor_valid(u8 bank, u8 id) > { > - if (parity8(bank) == 0 || parity8(id) == 0) > + if (!parity_odd(bank) || !parity_odd(id)) > return false; > > id &= 0x7f; > diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c > index 611c22b72c15..dc61d87fcd94 100644 > --- a/drivers/i3c/master/dw-i3c-master.c > +++ b/drivers/i3c/master/dw-i3c-master.c > @@ -867,7 +867,7 @@ static int dw_i3c_master_daa(struct i3c_master_controller *m) > master->devs[pos].addr = ret; > last_addr = ret; > > - ret |= parity8(ret) ? 0 : BIT(7); > + ret |= parity_odd(ret) ? 0 : BIT(7); > > writel(DEV_ADDR_TABLE_DYNAMIC_ADDR(ret), > master->regs + > diff --git a/drivers/i3c/master/i3c-master-cdns.c b/drivers/i3c/master/i3c-master-cdns.c > index fd3752cea654..df14f978a388 100644 > --- a/drivers/i3c/master/i3c-master-cdns.c > +++ b/drivers/i3c/master/i3c-master-cdns.c > @@ -889,7 +889,7 @@ static u32 prepare_rr0_dev_address(u32 addr) > ret |= (addr & GENMASK(9, 7)) << 6; > > /* RR0[0] = ~XOR(addr[6:0]) */ > - ret |= parity8(addr & 0x7f) ? 0 : BIT(0); > + ret |= parity_odd(addr & 0x7f) ? 0 : BIT(0); > > return ret; > } > diff --git a/drivers/i3c/master/mipi-i3c-hci/dat_v1.c b/drivers/i3c/master/mipi-i3c-hci/dat_v1.c > index 85c4916972e4..d692a299607d 100644 > --- a/drivers/i3c/master/mipi-i3c-hci/dat_v1.c > +++ b/drivers/i3c/master/mipi-i3c-hci/dat_v1.c > @@ -114,7 +114,7 @@ static void hci_dat_v1_set_dynamic_addr(struct i3c_hci *hci, > dat_w0 = dat_w0_read(dat_idx); > dat_w0 &= ~(DAT_0_DYNAMIC_ADDRESS | DAT_0_DYNADDR_PARITY); > dat_w0 |= FIELD_PREP(DAT_0_DYNAMIC_ADDRESS, address) | > - (parity8(address) ? 0 : DAT_0_DYNADDR_PARITY); > + (parity_odd(address) ? 0 : DAT_0_DYNADDR_PARITY); > dat_w0_write(dat_idx, dat_w0); > } > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index c1cb53cf2f0f..7c4c8afccef1 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -230,35 +230,40 @@ static inline int get_count_order_long(unsigned long l) > } > > /** > - * parity8 - get the parity of an u8 value > - * @value: the value to be examined > + * parity_odd - get the parity of an u64 value > + * @val: the value to be examined > * > - * Determine the parity of the u8 argument. > + * Determine the parity of the u64 argument. > * > * Returns: > - * 0 for even parity, 1 for odd parity > + * false for even parity, true for odd parity > * > * Note: This function informs you about the current parity. Example to bail > * out when parity is odd: > * > - * if (parity8(val) == 1) > + * if (parity_odd(val)) > * return -EBADMSG; > * > * If you need to calculate a parity bit, you need to draw the conclusion from > * this result yourself. Example to enforce odd parity, parity bit is bit 7: > * > - * if (parity8(val) == 0) > + * if (!parity_odd(val)) > * val ^= BIT(7); > */ > -static inline int parity8(u8 val) > +#ifndef parity_odd Please don't add this guard. We've got no any arch implementations so far, and this is a dead code. Those adding arch code will also add the ifdefery. > +static inline __attribute_const__ bool parity_odd(u64 val) > { > /* > * One explanation of this algorithm: > * https://funloop.org/codex/problem/parity/README.html > */ > + val ^= val >> 32; > + val ^= val >> 16; > + val ^= val >> 8; > val ^= val >> 4; > return (0x6996 >> (val & 0xf)) & 1; > } > +#endif > > /** > * __ffs64 - find first set bit in a 64 bit word > -- > 2.34.1
On Wed, Apr 09, 2025 at 12:59:14PM -0400, Yury Norov wrote: > On Wed, Apr 09, 2025 at 11:43:44PM +0800, Kuan-Wei Chiu wrote: > > Redesign the parity8() helper as parity_odd(), changing its input type > > from u8 to u64 to support broader use cases and its return type from > > int to bool to clearly reflect the function's binary output. The > > function now returns true for odd parity and false for even parity, > > making its behavior more intuitive based on the name. > > > > Also mark the function with __attribute_const__ to enable better > > compiler optimization, as the result depends solely on its input and > > has no side effects. > > > > While more efficient implementations may exist, further optimization is > > postponed until a use case in performance-critical paths arises. > > > > Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com> > > Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com> > > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com> > > --- > > arch/x86/kernel/bootflag.c | 4 ++-- > > drivers/hwmon/spd5118.c | 2 +- > > drivers/i3c/master/dw-i3c-master.c | 2 +- > > drivers/i3c/master/i3c-master-cdns.c | 2 +- > > drivers/i3c/master/mipi-i3c-hci/dat_v1.c | 2 +- > > include/linux/bitops.h | 19 ++++++++++++------- > > 6 files changed, 18 insertions(+), 13 deletions(-) > > > > diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c > > index 73274d76ce16..86aae4b2bfd5 100644 > > --- a/arch/x86/kernel/bootflag.c > > +++ b/arch/x86/kernel/bootflag.c > > @@ -26,7 +26,7 @@ static void __init sbf_write(u8 v) > > unsigned long flags; > > > > if (sbf_port != -1) { > > - if (!parity8(v)) > > + if (!parity_odd(v)) > > v ^= SBF_PARITY; > > > > printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n", > > @@ -57,7 +57,7 @@ static bool __init sbf_value_valid(u8 v) > > { > > if (v & SBF_RESERVED) /* Reserved bits */ > > return false; > > - if (!parity8(v)) > > + if (!parity_odd(v)) > > return false; > > > > return true; > > diff --git a/drivers/hwmon/spd5118.c b/drivers/hwmon/spd5118.c > > index 358152868d96..15761f2ca4e9 100644 > > --- a/drivers/hwmon/spd5118.c > > +++ b/drivers/hwmon/spd5118.c > > @@ -298,7 +298,7 @@ static umode_t spd5118_is_visible(const void *_data, enum hwmon_sensor_types typ > > */ > > static bool spd5118_vendor_valid(u8 bank, u8 id) > > { > > - if (parity8(bank) == 0 || parity8(id) == 0) > > + if (!parity_odd(bank) || !parity_odd(id)) > > return false; > > > > id &= 0x7f; > > diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c > > index 611c22b72c15..dc61d87fcd94 100644 > > --- a/drivers/i3c/master/dw-i3c-master.c > > +++ b/drivers/i3c/master/dw-i3c-master.c > > @@ -867,7 +867,7 @@ static int dw_i3c_master_daa(struct i3c_master_controller *m) > > master->devs[pos].addr = ret; > > last_addr = ret; > > > > - ret |= parity8(ret) ? 0 : BIT(7); > > + ret |= parity_odd(ret) ? 0 : BIT(7); > > > > writel(DEV_ADDR_TABLE_DYNAMIC_ADDR(ret), > > master->regs + > > diff --git a/drivers/i3c/master/i3c-master-cdns.c b/drivers/i3c/master/i3c-master-cdns.c > > index fd3752cea654..df14f978a388 100644 > > --- a/drivers/i3c/master/i3c-master-cdns.c > > +++ b/drivers/i3c/master/i3c-master-cdns.c > > @@ -889,7 +889,7 @@ static u32 prepare_rr0_dev_address(u32 addr) > > ret |= (addr & GENMASK(9, 7)) << 6; > > > > /* RR0[0] = ~XOR(addr[6:0]) */ > > - ret |= parity8(addr & 0x7f) ? 0 : BIT(0); > > + ret |= parity_odd(addr & 0x7f) ? 0 : BIT(0); > > > > return ret; > > } > > diff --git a/drivers/i3c/master/mipi-i3c-hci/dat_v1.c b/drivers/i3c/master/mipi-i3c-hci/dat_v1.c > > index 85c4916972e4..d692a299607d 100644 > > --- a/drivers/i3c/master/mipi-i3c-hci/dat_v1.c > > +++ b/drivers/i3c/master/mipi-i3c-hci/dat_v1.c > > @@ -114,7 +114,7 @@ static void hci_dat_v1_set_dynamic_addr(struct i3c_hci *hci, > > dat_w0 = dat_w0_read(dat_idx); > > dat_w0 &= ~(DAT_0_DYNAMIC_ADDRESS | DAT_0_DYNADDR_PARITY); > > dat_w0 |= FIELD_PREP(DAT_0_DYNAMIC_ADDRESS, address) | > > - (parity8(address) ? 0 : DAT_0_DYNADDR_PARITY); > > + (parity_odd(address) ? 0 : DAT_0_DYNADDR_PARITY); > > dat_w0_write(dat_idx, dat_w0); > > } > > > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > > index c1cb53cf2f0f..7c4c8afccef1 100644 > > --- a/include/linux/bitops.h > > +++ b/include/linux/bitops.h > > @@ -230,35 +230,40 @@ static inline int get_count_order_long(unsigned long l) > > } > > > > /** > > - * parity8 - get the parity of an u8 value > > - * @value: the value to be examined > > + * parity_odd - get the parity of an u64 value > > + * @val: the value to be examined > > * > > - * Determine the parity of the u8 argument. > > + * Determine the parity of the u64 argument. > > * > > * Returns: > > - * 0 for even parity, 1 for odd parity > > + * false for even parity, true for odd parity > > * > > * Note: This function informs you about the current parity. Example to bail > > * out when parity is odd: > > * > > - * if (parity8(val) == 1) > > + * if (parity_odd(val)) > > * return -EBADMSG; > > * > > * If you need to calculate a parity bit, you need to draw the conclusion from > > * this result yourself. Example to enforce odd parity, parity bit is bit 7: > > * > > - * if (parity8(val) == 0) > > + * if (!parity_odd(val)) > > * val ^= BIT(7); > > */ > > -static inline int parity8(u8 val) > > +#ifndef parity_odd > > Please don't add this guard. We've got no any arch implementations > so far, and this is a dead code. Those adding arch code will also > add the ifdefery. > Ack. Will do in next version. Regards, Kuan-Wei > > +static inline __attribute_const__ bool parity_odd(u64 val) > > { > > /* > > * One explanation of this algorithm: > > * https://funloop.org/codex/problem/parity/README.html > > */ > > + val ^= val >> 32; > > + val ^= val >> 16; > > + val ^= val >> 8; > > val ^= val >> 4; > > return (0x6996 >> (val & 0xf)) & 1; > > } > > +#endif > > > > /** > > * __ffs64 - find first set bit in a 64 bit word > > -- > > 2.34.1
On 4/9/25 11:25, Kuan-Wei Chiu wrote: > On Wed, Apr 09, 2025 at 12:59:14PM -0400, Yury Norov wrote: >> On Wed, Apr 09, 2025 at 11:43:44PM +0800, Kuan-Wei Chiu wrote: >>> Redesign the parity8() helper as parity_odd(), changing its input type >>> from u8 to u64 to support broader use cases and its return type from >>> int to bool to clearly reflect the function's binary output. The >>> function now returns true for odd parity and false for even parity, >>> making its behavior more intuitive based on the name. >>> >>> Also mark the function with __attribute_const__ to enable better >>> compiler optimization, as the result depends solely on its input and >>> has no side effects. >>> >>> While more efficient implementations may exist, further optimization is >>> postponed until a use case in performance-critical paths arises. >>> >>> Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com> >>> Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com> >>> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com> >>> --- >>> arch/x86/kernel/bootflag.c | 4 ++-- >>> drivers/hwmon/spd5118.c | 2 +- >>> drivers/i3c/master/dw-i3c-master.c | 2 +- >>> drivers/i3c/master/i3c-master-cdns.c | 2 +- >>> drivers/i3c/master/mipi-i3c-hci/dat_v1.c | 2 +- >>> include/linux/bitops.h | 19 ++++++++++++------- >>> 6 files changed, 18 insertions(+), 13 deletions(-) >>> >>> diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c >>> index 73274d76ce16..86aae4b2bfd5 100644 >>> --- a/arch/x86/kernel/bootflag.c >>> +++ b/arch/x86/kernel/bootflag.c >>> @@ -26,7 +26,7 @@ static void __init sbf_write(u8 v) >>> unsigned long flags; >>> >>> if (sbf_port != -1) { >>> - if (!parity8(v)) >>> + if (!parity_odd(v)) What is the benefit of this change all over the place instead of adding parity_odd() as new API and keeping the old one (just letting it call the new API) ? A simple static inline int parity8(u8 val) { return parity_odd(val); } would have done the trick and be much less invasive. Guenter
On Wed, Apr 09, 2025 at 11:39:22AM -0700, Guenter Roeck wrote: > On 4/9/25 11:25, Kuan-Wei Chiu wrote: > > On Wed, Apr 09, 2025 at 12:59:14PM -0400, Yury Norov wrote: > > > On Wed, Apr 09, 2025 at 11:43:44PM +0800, Kuan-Wei Chiu wrote: > > > > Redesign the parity8() helper as parity_odd(), changing its input type > > > > from u8 to u64 to support broader use cases and its return type from > > > > int to bool to clearly reflect the function's binary output. The > > > > function now returns true for odd parity and false for even parity, > > > > making its behavior more intuitive based on the name. > > > > > > > > Also mark the function with __attribute_const__ to enable better > > > > compiler optimization, as the result depends solely on its input and > > > > has no side effects. > > > > > > > > While more efficient implementations may exist, further optimization is > > > > postponed until a use case in performance-critical paths arises. > > > > > > > > Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com> > > > > Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com> > > > > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com> > > > > --- > > > > arch/x86/kernel/bootflag.c | 4 ++-- > > > > drivers/hwmon/spd5118.c | 2 +- > > > > drivers/i3c/master/dw-i3c-master.c | 2 +- > > > > drivers/i3c/master/i3c-master-cdns.c | 2 +- > > > > drivers/i3c/master/mipi-i3c-hci/dat_v1.c | 2 +- > > > > include/linux/bitops.h | 19 ++++++++++++------- > > > > 6 files changed, 18 insertions(+), 13 deletions(-) > > > > > > > > diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c > > > > index 73274d76ce16..86aae4b2bfd5 100644 > > > > --- a/arch/x86/kernel/bootflag.c > > > > +++ b/arch/x86/kernel/bootflag.c > > > > @@ -26,7 +26,7 @@ static void __init sbf_write(u8 v) > > > > unsigned long flags; > > > > if (sbf_port != -1) { > > > > - if (!parity8(v)) > > > > + if (!parity_odd(v)) > > What is the benefit of this change all over the place instead of > adding parity_odd() as new API and keeping the old one (just letting > it call the new API) ? > > A simple > > static inline int parity8(u8 val) > { > return parity_odd(val); > } > > would have done the trick and be much less invasive. > Yury has previously mentioned that adding multiple fixed-type parity functions increases his maintenance burden. IIUC, he prefers having a single interface in bitops.h rather than multiple ones. He were reluctant to add three more functions like: static inline bool parity16(u16 val) { return parity8(val ^ (val >> 8)); } static inline bool parity32(u32 val) { return parity16(val ^ (val >> 16)); } static inline bool parity64(u64 val) { return parity32(val ^ (val >> 32)); } But instead, we ended up with: static inline bool parity(u64 val) { val ^= val >> 32; val ^= val >> 16; val ^= val >> 8; val ^= val >> 4; return (0x6996 >> (val & 0xf)) & 1; } static inline bool parity8(u8 val) { return parity_odd(val); } But in the end, we introduced both parity(u64) and parity8(u8), which, IMHO, might be even more confusing than having consistent fixed-type helpers. Regards, Kuan-Wei
diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c index 73274d76ce16..86aae4b2bfd5 100644 --- a/arch/x86/kernel/bootflag.c +++ b/arch/x86/kernel/bootflag.c @@ -26,7 +26,7 @@ static void __init sbf_write(u8 v) unsigned long flags; if (sbf_port != -1) { - if (!parity8(v)) + if (!parity_odd(v)) v ^= SBF_PARITY; printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n", @@ -57,7 +57,7 @@ static bool __init sbf_value_valid(u8 v) { if (v & SBF_RESERVED) /* Reserved bits */ return false; - if (!parity8(v)) + if (!parity_odd(v)) return false; return true; diff --git a/drivers/hwmon/spd5118.c b/drivers/hwmon/spd5118.c index 358152868d96..15761f2ca4e9 100644 --- a/drivers/hwmon/spd5118.c +++ b/drivers/hwmon/spd5118.c @@ -298,7 +298,7 @@ static umode_t spd5118_is_visible(const void *_data, enum hwmon_sensor_types typ */ static bool spd5118_vendor_valid(u8 bank, u8 id) { - if (parity8(bank) == 0 || parity8(id) == 0) + if (!parity_odd(bank) || !parity_odd(id)) return false; id &= 0x7f; diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c index 611c22b72c15..dc61d87fcd94 100644 --- a/drivers/i3c/master/dw-i3c-master.c +++ b/drivers/i3c/master/dw-i3c-master.c @@ -867,7 +867,7 @@ static int dw_i3c_master_daa(struct i3c_master_controller *m) master->devs[pos].addr = ret; last_addr = ret; - ret |= parity8(ret) ? 0 : BIT(7); + ret |= parity_odd(ret) ? 0 : BIT(7); writel(DEV_ADDR_TABLE_DYNAMIC_ADDR(ret), master->regs + diff --git a/drivers/i3c/master/i3c-master-cdns.c b/drivers/i3c/master/i3c-master-cdns.c index fd3752cea654..df14f978a388 100644 --- a/drivers/i3c/master/i3c-master-cdns.c +++ b/drivers/i3c/master/i3c-master-cdns.c @@ -889,7 +889,7 @@ static u32 prepare_rr0_dev_address(u32 addr) ret |= (addr & GENMASK(9, 7)) << 6; /* RR0[0] = ~XOR(addr[6:0]) */ - ret |= parity8(addr & 0x7f) ? 0 : BIT(0); + ret |= parity_odd(addr & 0x7f) ? 0 : BIT(0); return ret; } diff --git a/drivers/i3c/master/mipi-i3c-hci/dat_v1.c b/drivers/i3c/master/mipi-i3c-hci/dat_v1.c index 85c4916972e4..d692a299607d 100644 --- a/drivers/i3c/master/mipi-i3c-hci/dat_v1.c +++ b/drivers/i3c/master/mipi-i3c-hci/dat_v1.c @@ -114,7 +114,7 @@ static void hci_dat_v1_set_dynamic_addr(struct i3c_hci *hci, dat_w0 = dat_w0_read(dat_idx); dat_w0 &= ~(DAT_0_DYNAMIC_ADDRESS | DAT_0_DYNADDR_PARITY); dat_w0 |= FIELD_PREP(DAT_0_DYNAMIC_ADDRESS, address) | - (parity8(address) ? 0 : DAT_0_DYNADDR_PARITY); + (parity_odd(address) ? 0 : DAT_0_DYNADDR_PARITY); dat_w0_write(dat_idx, dat_w0); } diff --git a/include/linux/bitops.h b/include/linux/bitops.h index c1cb53cf2f0f..7c4c8afccef1 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -230,35 +230,40 @@ static inline int get_count_order_long(unsigned long l) } /** - * parity8 - get the parity of an u8 value - * @value: the value to be examined + * parity_odd - get the parity of an u64 value + * @val: the value to be examined * - * Determine the parity of the u8 argument. + * Determine the parity of the u64 argument. * * Returns: - * 0 for even parity, 1 for odd parity + * false for even parity, true for odd parity * * Note: This function informs you about the current parity. Example to bail * out when parity is odd: * - * if (parity8(val) == 1) + * if (parity_odd(val)) * return -EBADMSG; * * If you need to calculate a parity bit, you need to draw the conclusion from * this result yourself. Example to enforce odd parity, parity bit is bit 7: * - * if (parity8(val) == 0) + * if (!parity_odd(val)) * val ^= BIT(7); */ -static inline int parity8(u8 val) +#ifndef parity_odd +static inline __attribute_const__ bool parity_odd(u64 val) { /* * One explanation of this algorithm: * https://funloop.org/codex/problem/parity/README.html */ + val ^= val >> 32; + val ^= val >> 16; + val ^= val >> 8; val ^= val >> 4; return (0x6996 >> (val & 0xf)) & 1; } +#endif /** * __ffs64 - find first set bit in a 64 bit word