| Message ID | 20240826204628.3541850-2-fanjason@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Subject: Support deposit8 in include/qemu/bitops.h | expand |
On Mon, 26 Aug 2024 at 22:01, Jason Fan <fanjason@google.com> wrote: > > Signed-off-by: Jason Fan <fanjason@google.com> > --- > include/qemu/bitops.h | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h > index 2c0a2fe751..d01c4b42f2 100644 > --- a/include/qemu/bitops.h > +++ b/include/qemu/bitops.h > @@ -459,6 +459,32 @@ static inline int64_t sextract64(uint64_t value, int start, int length) > return ((int64_t)(value << (64 - length - start))) >> (64 - length); > } > > +/** > + * deposit8: > + * @value: initial value to insert bit field into > + * @start: the lowest bit in the bit field (numbered from 0) > + * @length: the length of the bit field > + * @fieldval: the value to insert into the bit field > + * > + * Deposit @fieldval into the 8 bit @value at the bit field specified > + * by the @start and @length parameters, and return the modified > + * @value. Bits of @value outside the bit field are not modified. > + * Bits of @fieldval above the least significant @length bits are > + * ignored. The bit field must lie entirely within the 8 bit word. > + * It is valid to request that all 8 bits are modified (ie @length > + * 8 and @start 0). > + * > + * Returns: the modified @value. > + */ > +static inline uint8_t deposit8(uint8_t value, int start, int length, > + uint8_t fieldval) > +{ > + uint8_t mask = 0xFF; > + assert(start >= 0 && length > 0 && length <= 8 - start); > + mask = (mask >> (8 - length)) << start; > + return (value & ~mask) | ((fieldval << start) & mask); > +} What's the use case for this? Where would you need this and not be able to use "deposit32" instead? thanks -- PMM
Re-send this to include the original mail-list. Hi Peter, I am working on a i3c target model which requires bitops on the uint8_t registers. deposit8 can help to check incorrect length or start input for 8 bit value. You are right that desposit32 should also work if we always pass the correct arguments, but since the implementation seems trivial enough, I just go ahead and create the patch. Thank you. On Tue, Aug 27, 2024 at 2:23 AM Peter Maydell <peter.maydell@linaro.org> wrote: > On Mon, 26 Aug 2024 at 22:01, Jason Fan <fanjason@google.com> wrote: > > > > Signed-off-by: Jason Fan <fanjason@google.com> > > --- > > include/qemu/bitops.h | 26 ++++++++++++++++++++++++++ > > 1 file changed, 26 insertions(+) > > > > diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h > > index 2c0a2fe751..d01c4b42f2 100644 > > --- a/include/qemu/bitops.h > > +++ b/include/qemu/bitops.h > > @@ -459,6 +459,32 @@ static inline int64_t sextract64(uint64_t value, > int start, int length) > > return ((int64_t)(value << (64 - length - start))) >> (64 - length); > > } > > > > +/** > > + * deposit8: > > + * @value: initial value to insert bit field into > > + * @start: the lowest bit in the bit field (numbered from 0) > > + * @length: the length of the bit field > > + * @fieldval: the value to insert into the bit field > > + * > > + * Deposit @fieldval into the 8 bit @value at the bit field specified > > + * by the @start and @length parameters, and return the modified > > + * @value. Bits of @value outside the bit field are not modified. > > + * Bits of @fieldval above the least significant @length bits are > > + * ignored. The bit field must lie entirely within the 8 bit word. > > + * It is valid to request that all 8 bits are modified (ie @length > > + * 8 and @start 0). > > + * > > + * Returns: the modified @value. > > + */ > > +static inline uint8_t deposit8(uint8_t value, int start, int length, > > + uint8_t fieldval) > > +{ > > + uint8_t mask = 0xFF; > > + assert(start >= 0 && length > 0 && length <= 8 - start); > > + mask = (mask >> (8 - length)) << start; > > + return (value & ~mask) | ((fieldval << start) & mask); > > +} > > What's the use case for this? Where would you need this > and not be able to use "deposit32" instead? > > thanks > -- PMM >
On Wed, 28 Aug 2024 at 16:59, Jason Fan <fanjason@google.com> wrote: > > Re-send this to include the original mail-list. > > Hi Peter, > I am working on a i3c target model which requires bitops on the uint8_t registers. > deposit8 can help to check incorrect length or start input for 8 bit value. > You are right that desposit32 should also work if we always pass the correct arguments, but since the implementation seems trivial enough, I just go ahead and create the patch. Thanks. However I think by this argument we would want also deposit16, deposit24, deposit4 for 4-bit registers, and so on indefinitely. And your start and length arguments should be #defined constants, preferably done with the FIELD macros, not raw numbers, so I don't think that kind of bug is very likely. (Besides, even with a deposit8() it could protect against, say, a wrong start value that was 8 or greater, but not a wrong start value that happened to still be in range for a uint8_t.) -- PMM
diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h index 2c0a2fe751..d01c4b42f2 100644 --- a/include/qemu/bitops.h +++ b/include/qemu/bitops.h @@ -459,6 +459,32 @@ static inline int64_t sextract64(uint64_t value, int start, int length) return ((int64_t)(value << (64 - length - start))) >> (64 - length); } +/** + * deposit8: + * @value: initial value to insert bit field into + * @start: the lowest bit in the bit field (numbered from 0) + * @length: the length of the bit field + * @fieldval: the value to insert into the bit field + * + * Deposit @fieldval into the 8 bit @value at the bit field specified + * by the @start and @length parameters, and return the modified + * @value. Bits of @value outside the bit field are not modified. + * Bits of @fieldval above the least significant @length bits are + * ignored. The bit field must lie entirely within the 8 bit word. + * It is valid to request that all 8 bits are modified (ie @length + * 8 and @start 0). + * + * Returns: the modified @value. + */ +static inline uint8_t deposit8(uint8_t value, int start, int length, + uint8_t fieldval) +{ + uint8_t mask = 0xFF; + assert(start >= 0 && length > 0 && length <= 8 - start); + mask = (mask >> (8 - length)) << start; + return (value & ~mask) | ((fieldval << start) & mask); +} + /** * deposit32: * @value: initial value to insert bit field into
Signed-off-by: Jason Fan <fanjason@google.com> --- include/qemu/bitops.h | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+)