// picoChip ASM file // // Support for 16-bit unsigned division/modulus. // // Copyright (C) 2003-2014 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 // . .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 relevant 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