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// picoChip ASM file
//
// Support for 16-bit unsigned division/modulus.
//
// Copyright (C) 2003, 2004, 2005, 2008, 2009 Free Software Foundation, Inc.
// Contributed by Picochip Ltd.
// Maintained by Daniel Towner (daniel.towner@picochip.com)
//
// This file 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 3, or (at your option) any
// later version.
//
// This file 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.
//
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
//
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
.section .text
.global __divmod15
__divmod15:
_picoMark_FUNCTION_BEGIN=
// picoChip Function Prologue : &__divmod15 = 0 bytes
// The picoChip instruction set has a divstep instruction which
// is used to perform one iteration of a binary division algorithm.
// The instruction allows 16-bit signed division to be implemented.
// It does not directly allow 16-bit unsigned division to be
// implemented. Thus, this function pulls out the common division
// iteration for 15-bits unsigned, and then special wrappers
// provide the logic to change this into a 16-bit signed or
// unsigned division, as appropriate. This allows the two
// versions of division to share a common implementation, reducing
// code size when the two are used together. It also reduces
// the maintenance overhead.
// Input:
// r0 - dividend
// r1 - divisor
// Output:
// r0 - quotient
// r1 - remainder
// R5 is unused
// Check for special cases. The emphasis is on detecting these as
// quickly as possible, so that the main division can be started. If
// the user requests division by one, division by self, and so on
// then they will just have to accept that this won't be particularly
// quick (relatively), whereas a real division (e.g., dividing a
// large value by a small value) will run as fast as possible
// (i.e., special case detection should not slow down the common case)
//
// Special cases to consider:
//
// Division by zero.
// Division of zero.
// Inputs are equal
// Divisor is bigger than dividend
// Division by power of two (can be shifted instead).
// Division by 1 (special case of power of two division)
//
// Division/modulus by zero is undefined (ISO C:6.5.5), so
// don't bother handling this special case.
//
// The special cases of division by a power of 2 are ignored, since
// they cause the general case to slow down. Omitting these
// special cases also reduces code size considerably.
// Handle divisor >= dividend separately. Note that this also handles
// the case where the dividend is zero. Note that the flags must be
// preserved, since they are also used at the branch destination.
sub.0 r1,r0,r15
sbc r0,r2 \ bge divisorGeDividend
=-> sbc r1,r4
// Compute the shift count. The amount by which the divisor
// must be shifted left to be aligned with the dividend.
sub.0 r4,r2,r3
// Align the divisor to the dividend. Execute a divstep (since at
// least one will always be executed). Skip the remaining loop
// if the shift count is zero.
lsl.0 r1,r3,r1 \ beq skipLoop
=-> divstep r0,r1 \ add.1 r3,1,r2
// Execute the divstep loop until temp is 0. This assumes that the
// loop count is at least one.
sub.0 r3,1,r4
divLoop:
divstep r0,r1 \ bne divLoop
=-> sub.0 r4,1,r4
skipLoop:
// The top bits of the result are the remainder. The bottom
// bits are the quotient.
lsr.0 r0,r2,r1 \ sub.1 16,r2,r4
jr (lr ) \ lsl.0 r0,r4,r0
=-> lsr.0 r0,r4,r0
// Special case.
divisorGeDividend:
// The divisor is greater than or equal to the dividend. The flags
// indicate which of these alternatives it is. The COPYNE can be used
// to set the result appropriately, without introducing any more
// branches.
copy.0 r0,r1 \ copy.1 0,r0
jr (lr) \ copyeq r0,r1
=-> copyeq 1,r0
_picoMark_FUNCTION_END=
// picoChip Function Epilogue : __divmod15
//============================================================================
// All DWARF information between this marker, and the END OF DWARF
// marker should be included in the source file. Search for
// FUNCTION_STACK_SIZE_GOES_HERE and FUNCTION NAME GOES HERE, and
// provide the relevent information. Add markers called
// _picoMark_FUNCTION_BEGIN and _picoMark_FUNCTION_END around the
// function in question.
//============================================================================
//============================================================================
// Frame information.
//============================================================================
.section .debug_frame
_picoMark_DebugFrame=
// Common CIE header.
.unalignedInitLong _picoMark_CieEnd-_picoMark_CieBegin
_picoMark_CieBegin=
.unalignedInitLong 0xffffffff
.initByte 0x1 // CIE Version
.ascii 16#0# // CIE Augmentation
.uleb128 0x1 // CIE Code Alignment Factor
.sleb128 2 // CIE Data Alignment Factor
.initByte 0xc // CIE RA Column
.initByte 0xc // DW_CFA_def_cfa
.uleb128 0xd
.uleb128 0x0
.align 2
_picoMark_CieEnd=
// FDE
_picoMark_LSFDE0I900821033007563=
.unalignedInitLong _picoMark_FdeEnd-_picoMark_FdeBegin
_picoMark_FdeBegin=
.unalignedInitLong _picoMark_DebugFrame // FDE CIE offset
.unalignedInitWord _picoMark_FUNCTION_BEGIN // FDE initial location
.unalignedInitWord _picoMark_FUNCTION_END-_picoMark_FUNCTION_BEGIN
.initByte 0xe // DW_CFA_def_cfa_offset
.uleb128 0x0 // <-- FUNCTION_STACK_SIZE_GOES_HERE
.initByte 0x4 // DW_CFA_advance_loc4
.unalignedInitLong _picoMark_FUNCTION_END-_picoMark_FUNCTION_BEGIN
.initByte 0xe // DW_CFA_def_cfa_offset
.uleb128 0x0
.align 2
_picoMark_FdeEnd=
//============================================================================
// Abbrevation information.
//============================================================================
.section .debug_abbrev
_picoMark_ABBREVIATIONS=
.section .debug_abbrev
.uleb128 0x1 // (abbrev code)
.uleb128 0x11 // (TAG: DW_TAG_compile_unit)
.initByte 0x1 // DW_children_yes
.uleb128 0x10 // (DW_AT_stmt_list)
.uleb128 0x6 // (DW_FORM_data4)
.uleb128 0x12 // (DW_AT_high_pc)
.uleb128 0x1 // (DW_FORM_addr)
.uleb128 0x11 // (DW_AT_low_pc)
.uleb128 0x1 // (DW_FORM_addr)
.uleb128 0x25 // (DW_AT_producer)
.uleb128 0x8 // (DW_FORM_string)
.uleb128 0x13 // (DW_AT_language)
.uleb128 0x5 // (DW_FORM_data2)
.uleb128 0x3 // (DW_AT_name)
.uleb128 0x8 // (DW_FORM_string)
.initByte 0x0
.initByte 0x0
.uleb128 0x2 ;# (abbrev code)
.uleb128 0x2e ;# (TAG: DW_TAG_subprogram)
.initByte 0x0 ;# DW_children_no
.uleb128 0x3 ;# (DW_AT_name)
.uleb128 0x8 ;# (DW_FORM_string)
.uleb128 0x11 ;# (DW_AT_low_pc)
.uleb128 0x1 ;# (DW_FORM_addr)
.uleb128 0x12 ;# (DW_AT_high_pc)
.uleb128 0x1 ;# (DW_FORM_addr)
.initByte 0x0
.initByte 0x0
.initByte 0x0
//============================================================================
// Line information. DwarfLib requires this to be present, but it can
// be empty.
//============================================================================
.section .debug_line
_picoMark_LINES=
//============================================================================
// Debug Information
//============================================================================
.section .debug_info
//Fixed header.
.unalignedInitLong _picoMark_DEBUG_INFO_END-_picoMark_DEBUG_INFO_BEGIN
_picoMark_DEBUG_INFO_BEGIN=
.unalignedInitWord 0x2
.unalignedInitLong _picoMark_ABBREVIATIONS
.initByte 0x2
// Compile unit information.
.uleb128 0x1 // (DIE 0xb) DW_TAG_compile_unit)
.unalignedInitLong _picoMark_LINES
.unalignedInitWord _picoMark_FUNCTION_END
.unalignedInitWord _picoMark_FUNCTION_BEGIN
// Producer is `picoChip'
.ascii 16#70# 16#69# 16#63# 16#6f# 16#43# 16#68# 16#69# 16#70# 16#00#
.unalignedInitWord 0xcafe // ASM language
.ascii 16#0# // Name. DwarfLib expects this to be present.
.uleb128 0x2 ;# (DIE DW_TAG_subprogram)
// FUNCTION NAME GOES HERE. Use `echo name | od -t x1' to get the hex. Each hex
// digit is specified using the format 16#XX#
.ascii 16#5f# 16#64# 16#69# 16#76# 16#6d# 16#6f# 16#64# 16#31# 16#35# 16#0# // Function name `_divmod15'
.unalignedInitWord _picoMark_FUNCTION_BEGIN // DW_AT_low_pc
.unalignedInitWord _picoMark_FUNCTION_END // DW_AT_high_pc
.initByte 0x0 // end of compile unit children.
_picoMark_DEBUG_INFO_END=
//============================================================================
// END OF DWARF
//============================================================================
.section .endFile
// End of picoChip ASM file
|
