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Diffstat (limited to 'arch/c6x/lib/divu.S')
| -rw-r--r-- | arch/c6x/lib/divu.S | 98 |
1 files changed, 98 insertions, 0 deletions
diff --git a/arch/c6x/lib/divu.S b/arch/c6x/lib/divu.S new file mode 100644 index 000000000000..64af3c006dd3 --- /dev/null +++ b/arch/c6x/lib/divu.S @@ -0,0 +1,98 @@ +;; Copyright 2010 Free Software Foundation, Inc. +;; Contributed by Bernd Schmidt <bernds@codesourcery.com>. +;; +;; This program is free software; you can redistribute it and/or modify +;; it under the terms of the GNU General Public License as published by +;; the Free Software Foundation; either version 2 of the License, or +;; (at your option) any later version. +;; +;; This program is distributed in the hope that it will be useful, +;; but WITHOUT ANY WARRANTY; without even the implied warranty of +;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +;; GNU General Public License for more details. +;; +;; You should have received a copy of the GNU General Public License +;; along with this program; if not, write to the Free Software +;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + +#include <linux/linkage.h> + + ;; ABI considerations for the divide functions + ;; The following registers are call-used: + ;; __c6xabi_divi A0,A1,A2,A4,A6,B0,B1,B2,B4,B5 + ;; __c6xabi_divu A0,A1,A2,A4,A6,B0,B1,B2,B4 + ;; __c6xabi_remi A1,A2,A4,A5,A6,B0,B1,B2,B4 + ;; __c6xabi_remu A1,A4,A5,A7,B0,B1,B2,B4 + ;; + ;; In our implementation, divu and remu are leaf functions, + ;; while both divi and remi call into divu. + ;; A0 is not clobbered by any of the functions. + ;; divu does not clobber B2 either, which is taken advantage of + ;; in remi. + ;; divi uses B5 to hold the original return address during + ;; the call to divu. + ;; remi uses B2 and A5 to hold the input values during the + ;; call to divu. It stores B3 in on the stack. + + .text +ENTRY(__c6xabi_divu) + ;; We use a series of up to 31 subc instructions. First, we find + ;; out how many leading zero bits there are in the divisor. This + ;; gives us both a shift count for aligning (shifting) the divisor + ;; to the, and the number of times we have to execute subc. + + ;; At the end, we have both the remainder and most of the quotient + ;; in A4. The top bit of the quotient is computed first and is + ;; placed in A2. + + ;; Return immediately if the dividend is zero. + mv .s2x A4, B1 + [B1] lmbd .l2 1, B4, B1 +|| [!B1] b .s2 B3 ; RETURN A +|| [!B1] mvk .d2 1, B4 + mv .l1x B1, A6 +|| shl .s2 B4, B1, B4 + + ;; The loop performs a maximum of 28 steps, so we do the + ;; first 3 here. + cmpltu .l1x A4, B4, A2 + [!A2] sub .l1x A4, B4, A4 +|| shru .s2 B4, 1, B4 +|| xor .s1 1, A2, A2 + + shl .s1 A2, 31, A2 +|| [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + + ;; RETURN A may happen here (note: must happen before the next branch) +_divu_loop: + cmpgt .l2 B1, 7, B0 +|| [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 +|| [B0] b .s1 _divu_loop + [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + [B1] subc .l1x A4,B4,A4 +|| [B1] add .s2 -1, B1, B1 + ;; loop backwards branch happens here + + ret .s2 B3 +|| mvk .s1 32, A1 + sub .l1 A1, A6, A6 + shl .s1 A4, A6, A4 + shru .s1 A4, 1, A4 +|| sub .l1 A6, 1, A6 + or .l1 A2, A4, A4 + shru .s1 A4, A6, A4 + nop +ENDPROC(__c6xabi_divu) |