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86 lines
2.5 KiB
86 lines
2.5 KiB
;; SPDX-License-Identifier: GPL-2.0-or-later |
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;; Copyright 2010 Free Software Foundation, Inc. |
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;; Contributed by Bernd Schmidt <[email protected]>. |
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;; |
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#include <linux/linkage.h> |
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;; ABI considerations for the divide functions |
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;; The following registers are call-used: |
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;; __c6xabi_divi A0,A1,A2,A4,A6,B0,B1,B2,B4,B5 |
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;; __c6xabi_divu A0,A1,A2,A4,A6,B0,B1,B2,B4 |
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;; __c6xabi_remi A1,A2,A4,A5,A6,B0,B1,B2,B4 |
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;; __c6xabi_remu A1,A4,A5,A7,B0,B1,B2,B4 |
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;; |
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;; In our implementation, divu and remu are leaf functions, |
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;; while both divi and remi call into divu. |
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;; A0 is not clobbered by any of the functions. |
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;; divu does not clobber B2 either, which is taken advantage of |
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;; in remi. |
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;; divi uses B5 to hold the original return address during |
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;; the call to divu. |
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;; remi uses B2 and A5 to hold the input values during the |
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;; call to divu. It stores B3 in on the stack. |
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.text |
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ENTRY(__c6xabi_divu) |
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;; We use a series of up to 31 subc instructions. First, we find |
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;; out how many leading zero bits there are in the divisor. This |
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;; gives us both a shift count for aligning (shifting) the divisor |
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;; to the, and the number of times we have to execute subc. |
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;; At the end, we have both the remainder and most of the quotient |
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;; in A4. The top bit of the quotient is computed first and is |
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;; placed in A2. |
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;; Return immediately if the dividend is zero. |
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mv .s2x A4, B1 |
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[B1] lmbd .l2 1, B4, B1 |
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|| [!B1] b .s2 B3 ; RETURN A |
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|| [!B1] mvk .d2 1, B4 |
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mv .l1x B1, A6 |
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|| shl .s2 B4, B1, B4 |
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;; The loop performs a maximum of 28 steps, so we do the |
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;; first 3 here. |
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cmpltu .l1x A4, B4, A2 |
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[!A2] sub .l1x A4, B4, A4 |
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|| shru .s2 B4, 1, B4 |
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|| xor .s1 1, A2, A2 |
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shl .s1 A2, 31, A2 |
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|| [B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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[B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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;; RETURN A may happen here (note: must happen before the next branch) |
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_divu_loop: |
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cmpgt .l2 B1, 7, B0 |
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|| [B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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[B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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|| [B0] b .s1 _divu_loop |
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[B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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[B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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[B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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[B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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[B1] subc .l1x A4,B4,A4 |
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|| [B1] add .s2 -1, B1, B1 |
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;; loop backwards branch happens here |
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ret .s2 B3 |
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|| mvk .s1 32, A1 |
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sub .l1 A1, A6, A6 |
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shl .s1 A4, A6, A4 |
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shru .s1 A4, 1, A4 |
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|| sub .l1 A6, 1, A6 |
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or .l1 A2, A4, A4 |
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shru .s1 A4, A6, A4 |
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nop |
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ENDPROC(__c6xabi_divu)
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