Hi all,
How desirable/portable is it to use __int128 on non-x86 64-bit
architectures to get a 64*64 -> 128 bit multiply? On x86-64 this works
extremely well, but I'm worried about that needlessly breaking on other
architectures.
In particular, it looks opportune to use a scaling-by-multiply instead
of a multiply-divide on lines 253 and 269 of kernel/time.c:
243 unsigned int jiffies_to_msecs(const unsigned long j)
244 {
245 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
246 return (MSEC_PER_SEC / HZ) * j;
247 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
248 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
249 #else
250 # if BITS_PER_LONG == 32
251 return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
252 # else
253 return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
254 # endif
255 #endif
256 }
257 EXPORT_SYMBOL(jiffies_to_msecs);
258
259 unsigned int jiffies_to_usecs(const unsigned long j)
260 {
261 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
262 return (USEC_PER_SEC / HZ) * j;
263 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
264 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
265 #else
266 # if BITS_PER_LONG == 32
267 return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
268 # else
269 return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
270 # endif
271 #endif
272 }
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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