Latest news on "div" AFAIK: https://mail.mozilla.org/pipermail/es-discuss/2013-July/thread.html#32221
On Tue, Jul 8, 2014 at 10:45 AM, Filip Pizlo <[email protected]> wrote: > I like this a lot. > > It looks like it will have a fairly mellow performance cliff in cases > where VM optimizations fail for whatever reason, since even in a lower-tier > compiler incapable of sophisticated optimizations all you really have to do > is make sure that these new math function calls bottom out in something > efficient. > > This would be even better if there was a story for div and mod. Is there > one? > > -Filip > > > On Jul 8, 2014, at 7:59 AM, Fabrice Bellard <[email protected]> wrote: > > > > Hi all, > > > > Regarding 64 bit arithmetic, there is a simpler solution compared to > what was proposed in [1]. It is already possible to get the low 32 bit part > of the 64 bit operations for addition, subtraction and multiplication. So > it is enough to add a few more functions to get the high 32 bit part of 64 > bit additions, subtractions and multiplications. Hence I propose to add the > following functions: > > > > Math.iaddh(lo0, hi0, lo1, hi1) : return the high 32 bit part of the 64 > bit addition of (hi0, lo0) and (hi1, lo1). > > > > Math.isubh(lo0, hi0, lo1, hi1) : return the high 32 bit part of the 64 > bit subtraction of (hi0, lo0) and (hi1, lo1). > > > > Math.imulh(a, b) : return the high 32 bit part of the signed 64 bit > product of the 32 bit numbers a and b. > > > > Math.imuluh(a, b) : return the high 32 bit part of the unsigned 64 bit > product of the 32 bit numbers a and b. > > > > All these functions convert their argument to 32 bit integers. They > return a signed 32 bit integer. > > > > With these functions, the 64 bit operations are easy to implement : > > > > - (hi_res, lo_res) = (hi0, lo0) + (hi1, lo1) (64 bit addition): > > > > lo_res = (lo0 + lo1) | 0; > > hi_res = Math.iaddh(lo0, hi0, lo1, hi1); > > > > - (hi_res, lo_res) = (hi0, lo0) - (hi1, lo1) (64 bit subtraction): > > > > lo_res = (lo0 - lo1) | 0; > > hi_res = Math.isubh(lo0, hi0, lo1, hi1); > > > > - (hi_res, lo_res) = a * b (signed 64 bit product of 32 bit integers): > > > > lo_res = Math.imul(a, b); > > hi_res = Math.imulh(a, b); > > > > - (hi_res, lo_res) = a * b (unsigned 64 bit product of 32 bit integers): > > > > lo_res = Math.imul(a, b); > > hi_res = Math.imuluh(a, b); > > > > - (hi_res, lo_res) = (hi0, lo0) * (hi1, lo1) (signed 64 bit product of > 64 bit integers): > > > > lo_res = Math.imul(lo0, lo1); > > hi_res = (Math.imulh(lo0, lo1) + Math.imul(lo0, hi1)) | 0; > > hi_res = (hi_res + Math.imul(lo1, hi0)) | 0; > > > > - (hi_res, lo_res) = (hi0, lo0) * (hi1, lo1) (unsigned 64 bit product > of 64 bit integers): > > > > lo_res = Math.imul(lo0, lo1); > > hi_res = (Math.imuluh(lo0, lo1) + Math.imul(lo0, hi1)) | 0; > > hi_res = (hi_res + Math.imul(lo1, hi0)) | 0; > > > > It is easy for the compiler to optimize the code because only 32 bit > integers are used and because the functions have no side effect. Even if > the compiler does not remove the duplicate operation for the low 32 bit > parts, the overhead is very small on a 32 bit CPU (1 more instruction than > the optimal code). > > > > Fabrice. > > > > [1] https://www.mail-archive.com/es-discuss%40mozilla.org/msg27237.html > > _______________________________________________ > > es-discuss mailing list > > [email protected] > > https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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