262 lines
8.9 KiB
ArmAsm
262 lines
8.9 KiB
ArmAsm
// picoChip ASM file
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//
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// Support for 16-bit unsigned division/modulus.
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//
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// Copyright (C) 2003-2013 Free Software Foundation, Inc.
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// Contributed by Picochip Ltd.
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// Maintained by Daniel Towner (daniel.towner@picochip.com)
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//
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// This file is free software; you can redistribute it and/or modify it
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// under the terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option) any
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// later version.
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//
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// This file is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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//
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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.section .text
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.global __divmod15
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__divmod15:
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_picoMark_FUNCTION_BEGIN=
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// picoChip Function Prologue : &__divmod15 = 0 bytes
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// The picoChip instruction set has a divstep instruction which
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// is used to perform one iteration of a binary division algorithm.
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// The instruction allows 16-bit signed division to be implemented.
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// It does not directly allow 16-bit unsigned division to be
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// implemented. Thus, this function pulls out the common division
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// iteration for 15-bits unsigned, and then special wrappers
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// provide the logic to change this into a 16-bit signed or
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// unsigned division, as appropriate. This allows the two
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// versions of division to share a common implementation, reducing
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// code size when the two are used together. It also reduces
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// the maintenance overhead.
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// Input:
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// r0 - dividend
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// r1 - divisor
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// Output:
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// r0 - quotient
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// r1 - remainder
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// R5 is unused
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// Check for special cases. The emphasis is on detecting these as
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// quickly as possible, so that the main division can be started. If
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// the user requests division by one, division by self, and so on
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// then they will just have to accept that this won't be particularly
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// quick (relatively), whereas a real division (e.g., dividing a
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// large value by a small value) will run as fast as possible
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// (i.e., special case detection should not slow down the common case)
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//
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// Special cases to consider:
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//
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// Division by zero.
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// Division of zero.
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// Inputs are equal
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// Divisor is bigger than dividend
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// Division by power of two (can be shifted instead).
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// Division by 1 (special case of power of two division)
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//
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// Division/modulus by zero is undefined (ISO C:6.5.5), so
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// don't bother handling this special case.
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//
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// The special cases of division by a power of 2 are ignored, since
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// they cause the general case to slow down. Omitting these
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// special cases also reduces code size considerably.
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// Handle divisor >= dividend separately. Note that this also handles
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// the case where the dividend is zero. Note that the flags must be
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// preserved, since they are also used at the branch destination.
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sub.0 r1,r0,r15
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sbc r0,r2 \ bge divisorGeDividend
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=-> sbc r1,r4
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// Compute the shift count. The amount by which the divisor
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// must be shifted left to be aligned with the dividend.
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sub.0 r4,r2,r3
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// Align the divisor to the dividend. Execute a divstep (since at
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// least one will always be executed). Skip the remaining loop
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// if the shift count is zero.
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lsl.0 r1,r3,r1 \ beq skipLoop
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=-> divstep r0,r1 \ add.1 r3,1,r2
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// Execute the divstep loop until temp is 0. This assumes that the
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// loop count is at least one.
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sub.0 r3,1,r4
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divLoop:
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divstep r0,r1 \ bne divLoop
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=-> sub.0 r4,1,r4
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skipLoop:
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// The top bits of the result are the remainder. The bottom
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// bits are the quotient.
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lsr.0 r0,r2,r1 \ sub.1 16,r2,r4
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jr (lr ) \ lsl.0 r0,r4,r0
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=-> lsr.0 r0,r4,r0
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// Special case.
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divisorGeDividend:
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// The divisor is greater than or equal to the dividend. The flags
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// indicate which of these alternatives it is. The COPYNE can be used
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// to set the result appropriately, without introducing any more
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// branches.
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copy.0 r0,r1 \ copy.1 0,r0
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jr (lr) \ copyeq r0,r1
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=-> copyeq 1,r0
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_picoMark_FUNCTION_END=
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// picoChip Function Epilogue : __divmod15
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//============================================================================
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// All DWARF information between this marker, and the END OF DWARF
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// marker should be included in the source file. Search for
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// FUNCTION_STACK_SIZE_GOES_HERE and FUNCTION NAME GOES HERE, and
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// provide the relevant information. Add markers called
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// _picoMark_FUNCTION_BEGIN and _picoMark_FUNCTION_END around the
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// function in question.
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//============================================================================
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//============================================================================
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// Frame information.
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//============================================================================
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.section .debug_frame
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_picoMark_DebugFrame=
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// Common CIE header.
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.unalignedInitLong _picoMark_CieEnd-_picoMark_CieBegin
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_picoMark_CieBegin=
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.unalignedInitLong 0xffffffff
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.initByte 0x1 // CIE Version
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.ascii 16#0# // CIE Augmentation
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.uleb128 0x1 // CIE Code Alignment Factor
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.sleb128 2 // CIE Data Alignment Factor
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.initByte 0xc // CIE RA Column
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.initByte 0xc // DW_CFA_def_cfa
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.uleb128 0xd
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.uleb128 0x0
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.align 2
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_picoMark_CieEnd=
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// FDE
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_picoMark_LSFDE0I900821033007563=
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.unalignedInitLong _picoMark_FdeEnd-_picoMark_FdeBegin
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_picoMark_FdeBegin=
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.unalignedInitLong _picoMark_DebugFrame // FDE CIE offset
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.unalignedInitWord _picoMark_FUNCTION_BEGIN // FDE initial location
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.unalignedInitWord _picoMark_FUNCTION_END-_picoMark_FUNCTION_BEGIN
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.initByte 0xe // DW_CFA_def_cfa_offset
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.uleb128 0x0 // <-- FUNCTION_STACK_SIZE_GOES_HERE
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.initByte 0x4 // DW_CFA_advance_loc4
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.unalignedInitLong _picoMark_FUNCTION_END-_picoMark_FUNCTION_BEGIN
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.initByte 0xe // DW_CFA_def_cfa_offset
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.uleb128 0x0
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.align 2
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_picoMark_FdeEnd=
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//============================================================================
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// Abbrevation information.
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//============================================================================
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.section .debug_abbrev
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_picoMark_ABBREVIATIONS=
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.section .debug_abbrev
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.uleb128 0x1 // (abbrev code)
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.uleb128 0x11 // (TAG: DW_TAG_compile_unit)
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.initByte 0x1 // DW_children_yes
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.uleb128 0x10 // (DW_AT_stmt_list)
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.uleb128 0x6 // (DW_FORM_data4)
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.uleb128 0x12 // (DW_AT_high_pc)
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.uleb128 0x1 // (DW_FORM_addr)
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.uleb128 0x11 // (DW_AT_low_pc)
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.uleb128 0x1 // (DW_FORM_addr)
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.uleb128 0x25 // (DW_AT_producer)
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.uleb128 0x8 // (DW_FORM_string)
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.uleb128 0x13 // (DW_AT_language)
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.uleb128 0x5 // (DW_FORM_data2)
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.uleb128 0x3 // (DW_AT_name)
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.uleb128 0x8 // (DW_FORM_string)
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.initByte 0x0
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.initByte 0x0
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.uleb128 0x2 ;# (abbrev code)
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.uleb128 0x2e ;# (TAG: DW_TAG_subprogram)
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.initByte 0x0 ;# DW_children_no
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.uleb128 0x3 ;# (DW_AT_name)
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.uleb128 0x8 ;# (DW_FORM_string)
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.uleb128 0x11 ;# (DW_AT_low_pc)
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.uleb128 0x1 ;# (DW_FORM_addr)
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.uleb128 0x12 ;# (DW_AT_high_pc)
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.uleb128 0x1 ;# (DW_FORM_addr)
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.initByte 0x0
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.initByte 0x0
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.initByte 0x0
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//============================================================================
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// Line information. DwarfLib requires this to be present, but it can
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// be empty.
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//============================================================================
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.section .debug_line
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_picoMark_LINES=
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//============================================================================
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// Debug Information
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//============================================================================
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.section .debug_info
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//Fixed header.
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.unalignedInitLong _picoMark_DEBUG_INFO_END-_picoMark_DEBUG_INFO_BEGIN
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_picoMark_DEBUG_INFO_BEGIN=
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.unalignedInitWord 0x2
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.unalignedInitLong _picoMark_ABBREVIATIONS
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.initByte 0x2
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// Compile unit information.
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.uleb128 0x1 // (DIE 0xb) DW_TAG_compile_unit)
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.unalignedInitLong _picoMark_LINES
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.unalignedInitWord _picoMark_FUNCTION_END
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.unalignedInitWord _picoMark_FUNCTION_BEGIN
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// Producer is `picoChip'
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.ascii 16#70# 16#69# 16#63# 16#6f# 16#43# 16#68# 16#69# 16#70# 16#00#
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.unalignedInitWord 0xcafe // ASM language
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.ascii 16#0# // Name. DwarfLib expects this to be present.
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.uleb128 0x2 ;# (DIE DW_TAG_subprogram)
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// FUNCTION NAME GOES HERE. Use `echo name | od -t x1' to get the hex. Each hex
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// digit is specified using the format 16#XX#
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.ascii 16#5f# 16#64# 16#69# 16#76# 16#6d# 16#6f# 16#64# 16#31# 16#35# 16#0# // Function name `_divmod15'
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.unalignedInitWord _picoMark_FUNCTION_BEGIN // DW_AT_low_pc
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.unalignedInitWord _picoMark_FUNCTION_END // DW_AT_high_pc
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.initByte 0x0 // end of compile unit children.
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_picoMark_DEBUG_INFO_END=
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//============================================================================
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// END OF DWARF
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//============================================================================
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.section .endFile
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// End of picoChip ASM file
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