1 ;; SPDX-License-Identifier: GPL-2.0-or-later 2 ;; Copyright 2010 Free Software Foundation, Inc. 3 ;; Contributed by Bernd Schmidt <bernds@codesourcery.com>. 4 ;; 5 6 #include <linux/linkage.h> 7 8 ;; ABI considerations for the divide functions 9 ;; The following registers are call-used: 10 ;; __c6xabi_divi A0,A1,A2,A4,A6,B0,B1,B2,B4,B5 11 ;; __c6xabi_divu A0,A1,A2,A4,A6,B0,B1,B2,B4 12 ;; __c6xabi_remi A1,A2,A4,A5,A6,B0,B1,B2,B4 13 ;; __c6xabi_remu A1,A4,A5,A7,B0,B1,B2,B4 14 ;; 15 ;; In our implementation, divu and remu are leaf functions, 16 ;; while both divi and remi call into divu. 17 ;; A0 is not clobbered by any of the functions. 18 ;; divu does not clobber B2 either, which is taken advantage of 19 ;; in remi. 20 ;; divi uses B5 to hold the original return address during 21 ;; the call to divu. 22 ;; remi uses B2 and A5 to hold the input values during the 23 ;; call to divu. It stores B3 in on the stack. 24 25 .text 26 ENTRY(__c6xabi_divu) 27 ;; We use a series of up to 31 subc instructions. First, we find 28 ;; out how many leading zero bits there are in the divisor. This 29 ;; gives us both a shift count for aligning (shifting) the divisor 30 ;; to the, and the number of times we have to execute subc. 31 32 ;; At the end, we have both the remainder and most of the quotient 33 ;; in A4. The top bit of the quotient is computed first and is 34 ;; placed in A2. 35 36 ;; Return immediately if the dividend is zero. 37 mv .s2x A4, B1 38 [B1] lmbd .l2 1, B4, B1 39 || [!B1] b .s2 B3 ; RETURN A 40 || [!B1] mvk .d2 1, B4 41 mv .l1x B1, A6 42 || shl .s2 B4, B1, B4 43 44 ;; The loop performs a maximum of 28 steps, so we do the 45 ;; first 3 here. 46 cmpltu .l1x A4, B4, A2 47 [!A2] sub .l1x A4, B4, A4 48 || shru .s2 B4, 1, B4 49 || xor .s1 1, A2, A2 50 51 shl .s1 A2, 31, A2 52 || [B1] subc .l1x A4,B4,A4 53 || [B1] add .s2 -1, B1, B1 54 [B1] subc .l1x A4,B4,A4 55 || [B1] add .s2 -1, B1, B1 56 57 ;; RETURN A may happen here (note: must happen before the next branch) 58 _divu_loop: 59 cmpgt .l2 B1, 7, B0 60 || [B1] subc .l1x A4,B4,A4 61 || [B1] add .s2 -1, B1, B1 62 [B1] subc .l1x A4,B4,A4 63 || [B1] add .s2 -1, B1, B1 64 || [B0] b .s1 _divu_loop 65 [B1] subc .l1x A4,B4,A4 66 || [B1] add .s2 -1, B1, B1 67 [B1] subc .l1x A4,B4,A4 68 || [B1] add .s2 -1, B1, B1 69 [B1] subc .l1x A4,B4,A4 70 || [B1] add .s2 -1, B1, B1 71 [B1] subc .l1x A4,B4,A4 72 || [B1] add .s2 -1, B1, B1 73 [B1] subc .l1x A4,B4,A4 74 || [B1] add .s2 -1, B1, B1 75 ;; loop backwards branch happens here 76 77 ret .s2 B3 78 || mvk .s1 32, A1 79 sub .l1 A1, A6, A6 80 shl .s1 A4, A6, A4 81 shru .s1 A4, 1, A4 82 || sub .l1 A6, 1, A6 83 or .l1 A2, A4, A4 84 shru .s1 A4, A6, A4 85 nop 86 ENDPROC(__c6xabi_divu) 87