Re: [RFC][PATCH] do_div_signed()

[john stultz]

On Tue, 2007-05-22 at 13:52 +0200, Roman Zippel wrote:
> Hi,
> 
> On Mon, 21 May 2007, john stultz wrote:
> 
> > Here's a quick pass at adding do_div_signed() which provides a signed
> > version of do_div, avoiding having do_div users hack around signed
> > issues (like in ntp.c).
> > 
> > It probably could be optimized further, so let me know if you have any
> > suggestions.
> > 
> > 
> > Other thoughts?
> 
> Did I mention that this API could use a little cleanup? :)
> Below is what I had in mind, this makes it more clear what types the 
> functions are working on. As bonus I cleaned up the i386 div64 
> implementation to get rid of the ugly asm casts, so gcc can do better 
> register allocation and generate better code.
> 

Yep. Much nicer then mine!

thanks!
-john

> 
> Signed-off-by: Roman Zippel <zippel@xxxxxxxxxxxxxx>

Acked-by: John Stultz <johnstul@xxxxxxxxxx>


> ---
>  include/asm-generic/div64.h |   14 ++++++++++++++
>  include/asm-i386/div64.h    |   20 ++++++++++++++++++++
>  include/linux/calc64.h      |   28 ++++++++++++++++++++++++++++
>  kernel/time.c               |   26 +++++++-------------------
>  kernel/time/ntp.c           |   21 +++++----------------
>  lib/div64.c                 |   21 ++++++++++++++++++++-
>  6 files changed, 94 insertions(+), 36 deletions(-)
> 
> Index: linux-2.6/include/asm-generic/div64.h
> ===================================================================
> --- linux-2.6.orig/include/asm-generic/div64.h
> +++ linux-2.6/include/asm-generic/div64.h
> @@ -35,6 +35,20 @@ static inline uint64_t div64_64(uint64_t
>  	return dividend / divisor;
>  }
> 
> +static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
> +{
> +	*remainder = dividend % divisor;
> +	return dividend / divisor;
> +}
> +#define div_u64_rem	div_u64_rem
> +
> +static inline s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
> +{
> +	*remainder = dividend % divisor;
> +	return dividend / divisor;
> +}
> +#define div_s64_rem	div_s64_rem
> +
>  #elif BITS_PER_LONG == 32
> 
>  extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
> Index: linux-2.6/include/asm-i386/div64.h
> ===================================================================
> --- linux-2.6.orig/include/asm-i386/div64.h
> +++ linux-2.6/include/asm-i386/div64.h
> @@ -48,5 +48,25 @@ div_ll_X_l_rem(long long divs, long div,
> 
>  }
> 
> +static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
> +{
> +	union {
> +		u64 v64;
> +		u32 v32[2];
> +	} d = { dividend };
> +	u32 upper;
> +
> +	upper = d.v32[1];
> +	if (upper) {
> +		upper = d.v32[1] % divisor;
> +		d.v32[1] = d.v32[1] / divisor;
> +	}
> +	asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
> +		"rm" (divisor), "0" (d.v32[0]), "1" (upper));
> +	return d.v64;
> +}
> +#define div_u64_rem	div_u64_rem
> +
>  extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
> +
>  #endif
> Index: linux-2.6/include/linux/calc64.h
> ===================================================================
> --- linux-2.6.orig/include/linux/calc64.h
> +++ linux-2.6/include/linux/calc64.h
> @@ -46,4 +46,32 @@ static inline long div_long_long_rem_sig
>  	return res;
>  }
> 
> +#ifndef div_u64_rem
> +static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
> +{
> +	*remainder = do_div(dividend, divisor);
> +	return dividend;
> +}
> +#endif
> +
> +#ifndef div_u64
> +static inline u64 div_u64(u64 dividend, u32 divisor)
> +{
> +	u32 remainder;
> +	return div_u64_rem(dividend, divisor, &remainder);
> +}
> +#endif
> +
> +#ifndef div_s64_rem
> +extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);
> +#endif
> +
> +#ifndef div_s64
> +static inline s64 div_s64(s64 dividend, s32 divisor)
> +{
> +	s32 remainder;
> +	return div_s64_rem(dividend, divisor, &remainder);
> +}
> +#endif
> +
>  #endif
> Index: linux-2.6/kernel/time.c
> ===================================================================
> --- linux-2.6.orig/kernel/time.c
> +++ linux-2.6/kernel/time.c
> @@ -661,9 +661,7 @@ clock_t jiffies_to_clock_t(long x)
>  #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
>  	return x / (HZ / USER_HZ);
>  #else
> -	u64 tmp = (u64)x * TICK_NSEC;
> -	do_div(tmp, (NSEC_PER_SEC / USER_HZ));
> -	return (long)tmp;
> +	return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
>  #endif
>  }
>  EXPORT_SYMBOL(jiffies_to_clock_t);
> @@ -675,16 +673,12 @@ unsigned long clock_t_to_jiffies(unsigne
>  		return ~0UL;
>  	return x * (HZ / USER_HZ);
>  #else
> -	u64 jif;
> -
>  	/* Don't worry about loss of precision here .. */
>  	if (x >= ~0UL / HZ * USER_HZ)
>  		return ~0UL;
> 
>  	/* .. but do try to contain it here */
> -	jif = x * (u64) HZ;
> -	do_div(jif, USER_HZ);
> -	return jif;
> +	return div_u64((u64)x * HZ, USER_HZ);
>  #endif
>  }
>  EXPORT_SYMBOL(clock_t_to_jiffies);
> @@ -692,17 +686,15 @@ EXPORT_SYMBOL(clock_t_to_jiffies);
>  u64 jiffies_64_to_clock_t(u64 x)
>  {
>  #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
> -	do_div(x, HZ / USER_HZ);
> +	return div_u64(x, HZ / USER_HZ);
>  #else
>  	/*
>  	 * There are better ways that don't overflow early,
>  	 * but even this doesn't overflow in hundreds of years
>  	 * in 64 bits, so..
>  	 */
> -	x *= TICK_NSEC;
> -	do_div(x, (NSEC_PER_SEC / USER_HZ));
> +	return div_u64(x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
>  #endif
> -	return x;
>  }
> 
>  EXPORT_SYMBOL(jiffies_64_to_clock_t);
> @@ -710,21 +702,17 @@ EXPORT_SYMBOL(jiffies_64_to_clock_t);
>  u64 nsec_to_clock_t(u64 x)
>  {
>  #if (NSEC_PER_SEC % USER_HZ) == 0
> -	do_div(x, (NSEC_PER_SEC / USER_HZ));
> +	return div_u64(x, NSEC_PER_SEC / USER_HZ);
>  #elif (USER_HZ % 512) == 0
> -	x *= USER_HZ/512;
> -	do_div(x, (NSEC_PER_SEC / 512));
> +	return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
>  #else
>  	/*
>           * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
>           * overflow after 64.99 years.
>           * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
>           */
> -	x *= 9;
> -	do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2)) /
> -				  USER_HZ));
> +	return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
>  #endif
> -	return x;
>  }
> 
>  #if (BITS_PER_LONG < 64)
> Index: linux-2.6/kernel/time/ntp.c
> ===================================================================
> --- linux-2.6.orig/kernel/time/ntp.c
> +++ linux-2.6/kernel/time/ntp.c
> @@ -53,10 +53,8 @@ static void ntp_update_frequency(void)
> 
>  	tick_length_base = second_length;
> 
> -	do_div(second_length, HZ);
> -	tick_nsec = second_length >> TICK_LENGTH_SHIFT;
> -
> -	do_div(tick_length_base, NTP_INTERVAL_FREQ);
> +	tick_nsec = div_u64(second_length, HZ) >> TICK_LENGTH_SHIFT;
> +	tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
>  }
> 
>  /**
> @@ -197,7 +195,7 @@ void __attribute__ ((weak)) notify_arch_
>  int do_adjtimex(struct timex *txc)
>  {
>  	long mtemp, save_adjust, rem;
> -	s64 freq_adj, temp64;
> +	s64 freq_adj;
>  	int result;
> 
>  	/* In order to modify anything, you gotta be super-user! */
> @@ -300,17 +298,8 @@ int do_adjtimex(struct timex *txc)
>  		    freq_adj = time_offset * mtemp;
>  		    freq_adj = shift_right(freq_adj, time_constant * 2 +
>  					   (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
> -		    if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
> -			temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
> -			if (time_offset < 0) {
> -			    temp64 = -temp64;
> -			    do_div(temp64, mtemp);
> -			    freq_adj -= temp64;
> -			} else {
> -			    do_div(temp64, mtemp);
> -			    freq_adj += temp64;
> -			}
> -		    }
> +		    if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC))
> +			freq_adj += div_s64(time_offset << (SHIFT_NSEC - SHIFT_FLL), mtemp);
>  		    freq_adj += time_freq;
>  		    freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
>  		    time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
> Index: linux-2.6/lib/div64.c
> ===================================================================
> --- linux-2.6.orig/lib/div64.c
> +++ linux-2.6/lib/div64.c
> @@ -18,7 +18,7 @@
> 
>  #include <linux/types.h>
>  #include <linux/module.h>
> -#include <asm/div64.h>
> +#include <linux/calc64.h>
> 
>  /* Not needed on 64bit architectures */
>  #if BITS_PER_LONG == 32
> @@ -78,4 +78,23 @@ uint64_t div64_64(uint64_t dividend, uin
>  }
>  EXPORT_SYMBOL(div64_64);
> 
> +#ifndef div_s64_rem
> +s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
> +{
> +	u64 quotient;
> +
> +	if (dividend < 0) {
> +		quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
> +		*remainder = -*remainder;
> +		if (divisor > 0)
> +			quotient = -quotient;
> +	} else {
> +		quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
> +		if (divisor < 0)
> +			quotient = -quotient;
> +	}
> +	return quotient;
> +}
> +#endif
> +
>  #endif /* BITS_PER_LONG == 32 */

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