1 /* Copyright (C) 2004 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, write to the Free
16 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
22 /* 64-bit signed long remainder. These are not normal C functions. Argument
23 registers are t10 and t11, the result goes in t12. Only t12 and AT may
26 Theory of operation here is that we can use the FPU divider for virtually
27 all operands that we see: all dividend values between -2**53 and 2**53-1
28 can be computed directly. Note that divisor values need not be checked
29 against that range because the rounded fp value will be close enough such
30 that the quotient is < 1, which will properly be truncated to zero when we
31 convert back to integer.
33 When the dividend is outside the range for which we can compute exact
34 results, we use the fp quotent as an estimate from which we begin refining
35 an exact integral value. This reduces the number of iterations in the
36 shift-and-subtract loop significantly. */
41 .type __remq, @function
45 cfi_return_column (RA)
48 cfi_def_cfa_offset (FRAME)
51 /* Get the fp divide insn issued as quickly as possible. After
52 that's done, we have at least 22 cycles until its results are
53 ready -- all the time in the world to figure out how we're
54 going to use the results. */
61 cfi_rel_offset ($f0, 0)
62 cfi_rel_offset ($f1, 8)
70 /* Check to see if X fit in the double as an exact value. */
77 /* If we get here, we're expecting exact results from the division.
78 Do nothing else besides convert, compute remainder, clean up. */
88 cfi_def_cfa_offset (0)
97 /* If we get here, X is large enough that we don't expect exact
98 results, and neither X nor Y got mis-translated for the fp
99 division. Our task is to take the fp result, figure out how
100 far it's off from the correct result and compute a fixup. */
105 cfi_rel_offset (t0, 16)
106 cfi_rel_offset (t1, 24)
107 cfi_rel_offset (t2, 32)
108 cfi_rel_offset (t5, 40)
110 #define Q t0 /* quotient */
111 #define R RV /* remainder */
112 #define SY t1 /* scaled Y */
113 #define S t2 /* scalar */
114 #define QY t3 /* Q*Y */
116 /* The fixup code below can only handle unsigned values. */
131 cfi_rel_offset (t4, 8)
135 cfi_rel_offset (t3, 0)
152 bne t5, $fix_sign_out
166 cfi_def_cfa_offset (0)
171 /* The quotient that we computed was too large. We need to reduce
172 it by S such that Y*S >= R. Obviously the closer we get to the
173 correct value the better, but overshooting high is ok, as we'll
174 fix that up later. */
188 /* The quotient that we computed was too small. Divide Y by the
189 current remainder (R) and add that to the existing quotient (Q).
190 The expectation, of course, is that R is much smaller than X. */
191 /* Begin with a shift-up loop. Compute S such that Y*S >= R. We
192 already have a copy of Y in SY and the value 1 in S. */
200 /* Shift-down and subtract loop. Each iteration compares our scaled
201 Y (SY) with the remainder (R); if SY <= R then X is divisible by
202 Y's scalar (S) so add it to the quotient (Q). */
217 /* If we got here, then X|Y is negative. Need to adjust everything
218 such that we're doing unsigned division in the fixup loop. */
219 /* T5 records the changes we had to make:
220 bit 0: set if X was negated. Note that the sign of the
221 remainder follows the sign of the divisor.
222 bit 2: set if Y was negated.
234 bge t1, $fix_sign_in_ret1
244 /* Now we get to undo what we did above. */
245 /* ??? Is this really faster than just increasing the size of
246 the stack frame and storing X and Y in memory? */
259 .size __remq, .-__remq