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// picoChip ASM file
//
//   Support for 16-bit signed division/modulus.
//
//   Copyright (C) 2003, 2004, 2005, 2008, 2009  Free Software Foundation, Inc.
//   Contributed by picoChip Designs 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

.align 8                
.global __divmodhi4
__divmodhi4:
_picoMark_FUNCTION_BEGIN=

// picoChip Function Prologue : &__divmodhi4 = 4 bytes

        // 16-bit signed division. Most of the special cases are dealt
        // with by the 15-bit signed division library (e.g., division by
        // zero, division by 1, and so on). This wrapper simply inverts 
        // any negative inputs, calls the 15-bit library, and flips any
        // results as necessary.  The
        // only special cases to be handled here are where either the 
        // divisor or the dividend are the maximum negative values.

        // Encode r5 with a bit pattern which indicates whether the
        // outputs of the division must be negated. The MSB will be set
        // to the sign of the dividend (which controls the remainder's
        // sign), while the LSB will store the XOR of the two signs,
        // which indicates the quotient's sign. R5 is not modified by the
        // 15-bit divmod routine.
        sub.0 r1,16#8000#,r15 \ asr.1 r0,15,r4
        beq divisorIsLargestNegative \ lsr.0 r1,15,r3
=->     sub.0 r0,16#8000#,r15 \ xor.1 r3,r4,r5

        // Handle least negative dividend with a special case. Note that the
        // absolute value of the divisor is also computed here.
        add.0 [asr r1,15],r1,r3 \ beq dividendIsLargestNegative
=->     xor.0 [asr r1,15],r3,r1 \ stw lr,(fp)-1 
        
        // Compute the absolute value of the dividend, and call the main
        // divide routine.
        add.0 r4,r0,r2 \ jl (&__divmod15)  // fn_call &__divmod15
=->     xor.0 r4,r2,r0

handleNegatedResults:   
        // Speculatively store the negation of the results.
        sub.0 0,r0,r2 \ sub.1 0,r1,r3

        // Does the quotient need negating? The LSB indicates this.
        and.0 r5,1,r15 \ ldw (fp)-1,lr
        copyne r2,r0
                
        asr.0 r5,15,r15 \ jr (lr)
=->     copyne r3,r1
        
dividendIsLargestNegative:

        // Divide the constant -32768. Use the Hacker's Delight
        // algorithm (i.e., ((dividend / 2) / divisor) * 2) gives
        // approximate answer). This code is a special case, so no
        // great effort is made to make it fast, only to make it
        // small.

        lsr.0 r0,1,r0 \ jl (&__divmod15)  // fn_call &__divmod15
=->     stw r1,(fp)-2

        // Load the original divisor, and compute the new quotient and
        // remainder.   
        lsl.0 r0,1,r0 \ ldw (fp)-2,r3
        lsl.0 r1,1,r1 // Fill stall slot

        // The error in the quotient is 0 or 1. The error can be determined
        // by comparing the remainder to the original divisor. If the
        // remainder is bigger, then an error of 1 has been introduced,
        // which must be fixed.
        sub.0 r1,r3,r15
        blo noCompensationForError
=->     nop     
        add.0 r0,1,r0 \ sub.1 r1,r3,r1
noCompensationForError:
        bra handleNegatedResults
=->     nop

divisorIsLargestNegative:       
        // The flags indicate whether the dividend is also the maximum negative
        copy.0 r0,r1 \ copy.1 0,r0
        copyeq r0,r1 \ jr (lr)
=->     copyeq 1,r0

_picoMark_FUNCTION_END=
// picoChip Function Epilogue : __divmodhi4
        

//============================================================================
// 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 0x4    // <-- 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#68# 16#69# 16#34# 16#0# // Function name `_divmodhi4'
.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