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Diffstat (limited to 'arch/parisc/lib/milli/div_const.S')
| -rw-r--r-- | arch/parisc/lib/milli/div_const.S | 682 |
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diff --git a/arch/parisc/lib/milli/div_const.S b/arch/parisc/lib/milli/div_const.S deleted file mode 100644 index dd660076e944..000000000000 --- a/arch/parisc/lib/milli/div_const.S +++ /dev/null @@ -1,682 +0,0 @@ -/* 32 and 64-bit millicode, original author Hewlett-Packard - adapted for gcc by Paul Bame <bame@debian.org> - and Alan Modra <alan@linuxcare.com.au>. - - Copyright 2001, 2002, 2003 Free Software Foundation, Inc. - - This file is part of GCC and is released under the terms of - of the GNU General Public License as published by the Free Software - Foundation; either version 2, or (at your option) any later version. - See the file COPYING in the top-level GCC source directory for a copy - of the license. */ - -#include "milli.h" - -#ifdef L_div_const -/* ROUTINE: $$divI_2 - . $$divI_3 $$divU_3 - . $$divI_4 - . $$divI_5 $$divU_5 - . $$divI_6 $$divU_6 - . $$divI_7 $$divU_7 - . $$divI_8 - . $$divI_9 $$divU_9 - . $$divI_10 $$divU_10 - . - . $$divI_12 $$divU_12 - . - . $$divI_14 $$divU_14 - . $$divI_15 $$divU_15 - . $$divI_16 - . $$divI_17 $$divU_17 - . - . Divide by selected constants for single precision binary integers. - - INPUT REGISTERS: - . arg0 == dividend - . mrp == return pc - . sr0 == return space when called externally - - OUTPUT REGISTERS: - . arg0 = undefined - . arg1 = undefined - . ret1 = quotient - - OTHER REGISTERS AFFECTED: - . r1 = undefined - - SIDE EFFECTS: - . Causes a trap under the following conditions: NONE - . Changes memory at the following places: NONE - - PERMISSIBLE CONTEXT: - . Unwindable. - . Does not create a stack frame. - . Suitable for internal or external millicode. - . Assumes the special millicode register conventions. - - DISCUSSION: - . Calls other millicode routines using mrp: NONE - . Calls other millicode routines: NONE */ - - -/* TRUNCATED DIVISION BY SMALL INTEGERS - - We are interested in q(x) = floor(x/y), where x >= 0 and y > 0 - (with y fixed). - - Let a = floor(z/y), for some choice of z. Note that z will be - chosen so that division by z is cheap. - - Let r be the remainder(z/y). In other words, r = z - ay. - - Now, our method is to choose a value for b such that - - q'(x) = floor((ax+b)/z) - - is equal to q(x) over as large a range of x as possible. If the - two are equal over a sufficiently large range, and if it is easy to - form the product (ax), and it is easy to divide by z, then we can - perform the division much faster than the general division algorithm. - - So, we want the following to be true: - - . For x in the following range: - . - . ky <= x < (k+1)y - . - . implies that - . - . k <= (ax+b)/z < (k+1) - - We want to determine b such that this is true for all k in the - range {0..K} for some maximum K. - - Since (ax+b) is an increasing function of x, we can take each - bound separately to determine the "best" value for b. - - (ax+b)/z < (k+1) implies - - (a((k+1)y-1)+b < (k+1)z implies - - b < a + (k+1)(z-ay) implies - - b < a + (k+1)r - - This needs to be true for all k in the range {0..K}. In - particular, it is true for k = 0 and this leads to a maximum - acceptable value for b. - - b < a+r or b <= a+r-1 - - Taking the other bound, we have - - k <= (ax+b)/z implies - - k <= (aky+b)/z implies - - k(z-ay) <= b implies - - kr <= b - - Clearly, the largest range for k will be achieved by maximizing b, - when r is not zero. When r is zero, then the simplest choice for b - is 0. When r is not 0, set - - . b = a+r-1 - - Now, by construction, q'(x) = floor((ax+b)/z) = q(x) = floor(x/y) - for all x in the range: - - . 0 <= x < (K+1)y - - We need to determine what K is. Of our two bounds, - - . b < a+(k+1)r is satisfied for all k >= 0, by construction. - - The other bound is - - . kr <= b - - This is always true if r = 0. If r is not 0 (the usual case), then - K = floor((a+r-1)/r), is the maximum value for k. - - Therefore, the formula q'(x) = floor((ax+b)/z) yields the correct - answer for q(x) = floor(x/y) when x is in the range - - (0,(K+1)y-1) K = floor((a+r-1)/r) - - To be most useful, we want (K+1)y-1 = (max x) >= 2**32-1 so that - the formula for q'(x) yields the correct value of q(x) for all x - representable by a single word in HPPA. - - We are also constrained in that computing the product (ax), adding - b, and dividing by z must all be done quickly, otherwise we will be - better off going through the general algorithm using the DS - instruction, which uses approximately 70 cycles. - - For each y, there is a choice of z which satisfies the constraints - for (K+1)y >= 2**32. We may not, however, be able to satisfy the - timing constraints for arbitrary y. It seems that z being equal to - a power of 2 or a power of 2 minus 1 is as good as we can do, since - it minimizes the time to do division by z. We want the choice of z - to also result in a value for (a) that minimizes the computation of - the product (ax). This is best achieved if (a) has a regular bit - pattern (so the multiplication can be done with shifts and adds). - The value of (a) also needs to be less than 2**32 so the product is - always guaranteed to fit in 2 words. - - In actual practice, the following should be done: - - 1) For negative x, you should take the absolute value and remember - . the fact so that the result can be negated. This obviously does - . not apply in the unsigned case. - 2) For even y, you should factor out the power of 2 that divides y - . and divide x by it. You can then proceed by dividing by the - . odd factor of y. - - Here is a table of some odd values of y, and corresponding choices - for z which are "good". - - y z r a (hex) max x (hex) - - 3 2**32 1 55555555 100000001 - 5 2**32 1 33333333 100000003 - 7 2**24-1 0 249249 (infinite) - 9 2**24-1 0 1c71c7 (infinite) - 11 2**20-1 0 1745d (infinite) - 13 2**24-1 0 13b13b (infinite) - 15 2**32 1 11111111 10000000d - 17 2**32 1 f0f0f0f 10000000f - - If r is 1, then b = a+r-1 = a. This simplifies the computation - of (ax+b), since you can compute (x+1)(a) instead. If r is 0, - then b = 0 is ok to use which simplifies (ax+b). - - The bit patterns for 55555555, 33333333, and 11111111 are obviously - very regular. The bit patterns for the other values of a above are: - - y (hex) (binary) - - 7 249249 001001001001001001001001 << regular >> - 9 1c71c7 000111000111000111000111 << regular >> - 11 1745d 000000010111010001011101 << irregular >> - 13 13b13b 000100111011000100111011 << irregular >> - - The bit patterns for (a) corresponding to (y) of 11 and 13 may be - too irregular to warrant using this method. - - When z is a power of 2 minus 1, then the division by z is slightly - more complicated, involving an iterative solution. - - The code presented here solves division by 1 through 17, except for - 11 and 13. There are algorithms for both signed and unsigned - quantities given. - - TIMINGS (cycles) - - divisor positive negative unsigned - - . 1 2 2 2 - . 2 4 4 2 - . 3 19 21 19 - . 4 4 4 2 - . 5 18 22 19 - . 6 19 22 19 - . 8 4 4 2 - . 10 18 19 17 - . 12 18 20 18 - . 15 16 18 16 - . 16 4 4 2 - . 17 16 18 16 - - Now, the algorithm for 7, 9, and 14 is an iterative one. That is, - a loop body is executed until the tentative quotient is 0. The - number of times the loop body is executed varies depending on the - dividend, but is never more than two times. If the dividend is - less than the divisor, then the loop body is not executed at all. - Each iteration adds 4 cycles to the timings. - - divisor positive negative unsigned - - . 7 19+4n 20+4n 20+4n n = number of iterations - . 9 21+4n 22+4n 21+4n - . 14 21+4n 22+4n 20+4n - - To give an idea of how the number of iterations varies, here is a - table of dividend versus number of iterations when dividing by 7. - - smallest largest required - dividend dividend iterations - - . 0 6 0 - . 7 0x6ffffff 1 - 0x1000006 0xffffffff 2 - - There is some overlap in the range of numbers requiring 1 and 2 - iterations. */ - -RDEFINE(t2,r1) -RDEFINE(x2,arg0) /* r26 */ -RDEFINE(t1,arg1) /* r25 */ -RDEFINE(x1,ret1) /* r29 */ - - SUBSPA_MILLI_DIV - ATTR_MILLI - - .proc - .callinfo millicode - .entry -/* NONE of these routines require a stack frame - ALL of these routines are unwindable from millicode */ - -GSYM($$divide_by_constant) - .export $$divide_by_constant,millicode -/* Provides a "nice" label for the code covered by the unwind descriptor - for things like gprof. */ - -/* DIVISION BY 2 (shift by 1) */ -GSYM($$divI_2) - .export $$divI_2,millicode - comclr,>= arg0,0,0 - addi 1,arg0,arg0 - MILLIRET - extrs arg0,30,31,ret1 - - -/* DIVISION BY 4 (shift by 2) */ -GSYM($$divI_4) - .export $$divI_4,millicode - comclr,>= arg0,0,0 - addi 3,arg0,arg0 - MILLIRET - extrs arg0,29,30,ret1 - - -/* DIVISION BY 8 (shift by 3) */ -GSYM($$divI_8) - .export $$divI_8,millicode - comclr,>= arg0,0,0 - addi 7,arg0,arg0 - MILLIRET - extrs arg0,28,29,ret1 - -/* DIVISION BY 16 (shift by 4) */ -GSYM($$divI_16) - .export $$divI_16,millicode - comclr,>= arg0,0,0 - addi 15,arg0,arg0 - MILLIRET - extrs arg0,27,28,ret1 - -/**************************************************************************** -* -* DIVISION BY DIVISORS OF FFFFFFFF, and powers of 2 times these -* -* includes 3,5,15,17 and also 6,10,12 -* -****************************************************************************/ - -/* DIVISION BY 3 (use z = 2**32; a = 55555555) */ - -GSYM($$divI_3) - .export $$divI_3,millicode - comb,<,N x2,0,LREF(neg3) - - addi 1,x2,x2 /* this cannot overflow */ - extru x2,1,2,x1 /* multiply by 5 to get started */ - sh2add x2,x2,x2 - b LREF(pos) - addc x1,0,x1 - -LSYM(neg3) - subi 1,x2,x2 /* this cannot overflow */ - extru x2,1,2,x1 /* multiply by 5 to get started */ - sh2add x2,x2,x2 - b LREF(neg) - addc x1,0,x1 - -GSYM($$divU_3) - .export $$divU_3,millicode - addi 1,x2,x2 /* this CAN overflow */ - addc 0,0,x1 - shd x1,x2,30,t1 /* multiply by 5 to get started */ - sh2add x2,x2,x2 - b LREF(pos) - addc x1,t1,x1 - -/* DIVISION BY 5 (use z = 2**32; a = 33333333) */ - -GSYM($$divI_5) - .export $$divI_5,millicode - comb,<,N x2,0,LREF(neg5) - - addi 3,x2,t1 /* this cannot overflow */ - sh1add x2,t1,x2 /* multiply by 3 to get started */ - b LREF(pos) - addc 0,0,x1 - -LSYM(neg5) - sub 0,x2,x2 /* negate x2 */ - addi 1,x2,x2 /* this cannot overflow */ - shd 0,x2,31,x1 /* get top bit (can be 1) */ - sh1add x2,x2,x2 /* multiply by 3 to get started */ - b LREF(neg) - addc x1,0,x1 - -GSYM($$divU_5) - .export $$divU_5,millicode - addi 1,x2,x2 /* this CAN overflow */ - addc 0,0,x1 - shd x1,x2,31,t1 /* multiply by 3 to get started */ - sh1add x2,x2,x2 - b LREF(pos) - addc t1,x1,x1 - -/* DIVISION BY 6 (shift to divide by 2 then divide by 3) */ -GSYM($$divI_6) - .export $$divI_6,millicode - comb,<,N x2,0,LREF(neg6) - extru x2,30,31,x2 /* divide by 2 */ - addi 5,x2,t1 /* compute 5*(x2+1) = 5*x2+5 */ - sh2add x2,t1,x2 /* multiply by 5 to get started */ - b LREF(pos) - addc 0,0,x1 - -LSYM(neg6) - subi 2,x2,x2 /* negate, divide by 2, and add 1 */ - /* negation and adding 1 are done */ - /* at the same time by the SUBI */ - extru x2,30,31,x2 - shd 0,x2,30,x1 - sh2add x2,x2,x2 /* multiply by 5 to get started */ - b LREF(neg) - addc x1,0,x1 - -GSYM($$divU_6) - .export $$divU_6,millicode - extru x2,30,31,x2 /* divide by 2 */ - addi 1,x2,x2 /* cannot carry */ - shd 0,x2,30,x1 /* multiply by 5 to get started */ - sh2add x2,x2,x2 - b LREF(pos) - addc x1,0,x1 - -/* DIVISION BY 10 (shift to divide by 2 then divide by 5) */ -GSYM($$divU_10) - .export $$divU_10,millicode - extru x2,30,31,x2 /* divide by 2 */ - addi 3,x2,t1 /* compute 3*(x2+1) = (3*x2)+3 */ - sh1add x2,t1,x2 /* multiply by 3 to get started */ - addc 0,0,x1 -LSYM(pos) - shd x1,x2,28,t1 /* multiply by 0x11 */ - shd x2,0,28,t2 - add x2,t2,x2 - addc x1,t1,x1 -LSYM(pos_for_17) - shd x1,x2,24,t1 /* multiply by 0x101 */ - shd x2,0,24,t2 - add x2,t2,x2 - addc x1,t1,x1 - - shd x1,x2,16,t1 /* multiply by 0x10001 */ - shd x2,0,16,t2 - add x2,t2,x2 - MILLIRET - addc x1,t1,x1 - -GSYM($$divI_10) - .export $$divI_10,millicode - comb,< x2,0,LREF(neg10) - copy 0,x1 - extru x2,30,31,x2 /* divide by 2 */ - addib,TR 1,x2,LREF(pos) /* add 1 (cannot overflow) */ - sh1add x2,x2,x2 /* multiply by 3 to get started */ - -LSYM(neg10) - subi 2,x2,x2 /* negate, divide by 2, and add 1 */ - /* negation and adding 1 are done */ - /* at the same time by the SUBI */ - extru x2,30,31,x2 - sh1add x2,x2,x2 /* multiply by 3 to get started */ -LSYM(neg) - shd x1,x2,28,t1 /* multiply by 0x11 */ - shd x2,0,28,t2 - add x2,t2,x2 - addc x1,t1,x1 -LSYM(neg_for_17) - shd x1,x2,24,t1 /* multiply by 0x101 */ - shd x2,0,24,t2 - add x2,t2,x2 - addc x1,t1,x1 - - shd x1,x2,16,t1 /* multiply by 0x10001 */ - shd x2,0,16,t2 - add x2,t2,x2 - addc x1,t1,x1 - MILLIRET - sub 0,x1,x1 - -/* DIVISION BY 12 (shift to divide by 4 then divide by 3) */ -GSYM($$divI_12) - .export $$divI_12,millicode - comb,< x2,0,LREF(neg12) - copy 0,x1 - extru x2,29,30,x2 /* divide by 4 */ - addib,tr 1,x2,LREF(pos) /* compute 5*(x2+1) = 5*x2+5 */ - sh2add x2,x2,x2 /* multiply by 5 to get started */ - -LSYM(neg12) - subi 4,x2,x2 /* negate, divide by 4, and add 1 */ - /* negation and adding 1 are done */ - /* at the same time by the SUBI */ - extru x2,29,30,x2 - b LREF(neg) - sh2add x2,x2,x2 /* multiply by 5 to get started */ - -GSYM($$divU_12) - .export $$divU_12,millicode - extru x2,29,30,x2 /* divide by 4 */ - addi 5,x2,t1 /* cannot carry */ - sh2add x2,t1,x2 /* multiply by 5 to get started */ - b LREF(pos) - addc 0,0,x1 - -/* DIVISION BY 15 (use z = 2**32; a = 11111111) */ -GSYM($$divI_15) - .export $$divI_15,millicode - comb,< x2,0,LREF(neg15) - copy 0,x1 - addib,tr 1,x2,LREF(pos)+4 - shd x1,x2,28,t1 - -LSYM(neg15) - b LREF(neg) - subi 1,x2,x2 - -GSYM($$divU_15) - .export $$divU_15,millicode - addi 1,x2,x2 /* this CAN overflow */ - b LREF(pos) - addc 0,0,x1 - -/* DIVISION BY 17 (use z = 2**32; a = f0f0f0f) */ -GSYM($$divI_17) - .export $$divI_17,millicode - comb,<,n x2,0,LREF(neg17) - addi 1,x2,x2 /* this cannot overflow */ - shd 0,x2,28,t1 /* multiply by 0xf to get started */ - shd x2,0,28,t2 - sub t2,x2,x2 - b LREF(pos_for_17) - subb t1,0,x1 - -LSYM(neg17) - subi 1,x2,x2 /* this cannot overflow */ - shd 0,x2,28,t1 /* multiply by 0xf to get started */ - shd x2,0,28,t2 - sub t2,x2,x2 - b LREF(neg_for_17) - subb t1,0,x1 - -GSYM($$divU_17) - .export $$divU_17,millicode - addi 1,x2,x2 /* this CAN overflow */ - addc 0,0,x1 - shd x1,x2,28,t1 /* multiply by 0xf to get started */ -LSYM(u17) - shd x2,0,28,t2 - sub t2,x2,x2 - b LREF(pos_for_17) - subb t1,x1,x1 - - -/* DIVISION BY DIVISORS OF FFFFFF, and powers of 2 times these - includes 7,9 and also 14 - - - z = 2**24-1 - r = z mod x = 0 - - so choose b = 0 - - Also, in order to divide by z = 2**24-1, we approximate by dividing - by (z+1) = 2**24 (which is easy), and then correcting. - - (ax) = (z+1)q' + r - . = zq' + (q'+r) - - So to compute (ax)/z, compute q' = (ax)/(z+1) and r = (ax) mod (z+1) - Then the true remainder of (ax)/z is (q'+r). Repeat the process - with this new remainder, adding the tentative quotients together, - until a tentative quotient is 0 (and then we are done). There is - one last correction to be done. It is possible that (q'+r) = z. - If so, then (q'+r)/(z+1) = 0 and it looks like we are done. But, - in fact, we need to add 1 more to the quotient. Now, it turns - out that this happens if and only if the original value x is - an exact multiple of y. So, to avoid a three instruction test at - the end, instead use 1 instruction to add 1 to x at the beginning. */ - -/* DIVISION BY 7 (use z = 2**24-1; a = 249249) */ -GSYM($$divI_7) - .export $$divI_7,millicode - comb,<,n x2,0,LREF(neg7) -LSYM(7) - addi 1,x2,x2 /* cannot overflow */ - shd 0,x2,29,x1 - sh3add x2,x2,x2 - addc x1,0,x1 -LSYM(pos7) - shd x1,x2,26,t1 - shd x2,0,26,t2 - add x2,t2,x2 - addc x1,t1,x1 - - shd x1,x2,20,t1 - shd x2,0,20,t2 - add x2,t2,x2 - addc x1,t1,t1 - - /* computed <t1,x2>. Now divide it by (2**24 - 1) */ - - copy 0,x1 - shd,= t1,x2,24,t1 /* tentative quotient */ -LSYM(1) - addb,tr t1,x1,LREF(2) /* add to previous quotient */ - extru x2,31,24,x2 /* new remainder (unadjusted) */ - - MILLIRETN - -LSYM(2) - addb,tr t1,x2,LREF(1) /* adjust remainder */ - extru,= x2,7,8,t1 /* new quotient */ - -LSYM(neg7) - subi 1,x2,x2 /* negate x2 and add 1 */ -LSYM(8) - shd 0,x2,29,x1 - sh3add x2,x2,x2 - addc x1,0,x1 - -LSYM(neg7_shift) - shd x1,x2,26,t1 - shd x2,0,26,t2 - add x2,t2,x2 - addc x1,t1,x1 - - shd x1,x2,20,t1 - shd x2,0,20,t2 - add x2,t2,x2 - addc x1,t1,t1 - - /* computed <t1,x2>. Now divide it by (2**24 - 1) */ - - copy 0,x1 - shd,= t1,x2,24,t1 /* tentative quotient */ -LSYM(3) - addb,tr t1,x1,LREF(4) /* add to previous quotient */ - extru x2,31,24,x2 /* new remainder (unadjusted) */ - - MILLIRET - sub 0,x1,x1 /* negate result */ - -LSYM(4) - addb,tr t1,x2,LREF(3) /* adjust remainder */ - extru,= x2,7,8,t1 /* new quotient */ - -GSYM($$divU_7) - .export $$divU_7,millicode - addi 1,x2,x2 /* can carry */ - addc 0,0,x1 - shd x1,x2,29,t1 - sh3add x2,x2,x2 - b LREF(pos7) - addc t1,x1,x1 - -/* DIVISION BY 9 (use z = 2**24-1; a = 1c71c7) */ -GSYM($$divI_9) - .export $$divI_9,millicode - comb,<,n x2,0,LREF(neg9) - addi 1,x2,x2 /* cannot overflow */ - shd 0,x2,29,t1 - shd x2,0,29,t2 - sub t2,x2,x2 - b LREF(pos7) - subb t1,0,x1 - -LSYM(neg9) - subi 1,x2,x2 /* negate and add 1 */ - shd 0,x2,29,t1 - shd x2,0,29,t2 - sub t2,x2,x2 - b LREF(neg7_shift) - subb t1,0,x1 - -GSYM($$divU_9) - .export $$divU_9,millicode - addi 1,x2,x2 /* can carry */ - addc 0,0,x1 - shd x1,x2,29,t1 - shd x2,0,29,t2 - sub t2,x2,x2 - b LREF(pos7) - subb t1,x1,x1 - -/* DIVISION BY 14 (shift to divide by 2 then divide by 7) */ -GSYM($$divI_14) - .export $$divI_14,millicode - comb,<,n x2,0,LREF(neg14) -GSYM($$divU_14) - .export $$divU_14,millicode - b LREF(7) /* go to 7 case */ - extru x2,30,31,x2 /* divide by 2 */ - -LSYM(neg14) - subi 2,x2,x2 /* negate (and add 2) */ - b LREF(8) - extru x2,30,31,x2 /* divide by 2 */ - .exit - .procend - .end -#endif |
