libgcc/config/picochip/divmod15.S

   1 // picoChip ASM file
   2 //
   3 //   Support for 16-bit unsigned division/modulus.
   4 //
   5 //   Copyright (C) 2003, 2004, 2005, 2008, 2009  Free Software Foundation, Inc.
   6 //   Contributed by Picochip Ltd.
   7 //   Maintained by Daniel Towner (daniel.towner@picochip.com)
   8 //
   9 //   This file is free software; you can redistribute it and/or modify it
  10 //   under the terms of the GNU General Public License as published by the
  11 //   Free Software Foundation; either version 3, or (at your option) any
  12 //   later version.
  13 //
  14 //   This file is distributed in the hope that it will be useful, but
  15 //   WITHOUT ANY WARRANTY; without even the implied warranty of
  16 //   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17 //   General Public License for more details.
  18 //
  19 //   Under Section 7 of GPL version 3, you are granted additional
  20 //   permissions described in the GCC Runtime Library Exception, version
  21 //   3.1, as published by the Free Software Foundation.
  22 //
  23 //   You should have received a copy of the GNU General Public License and
  24 //   a copy of the GCC Runtime Library Exception along with this program;
  25 //   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  26 //   <http://www.gnu.org/licenses/>.
  27
  28 .section .text
  29
  30 .global __divmod15
  31 __divmod15:
  32 _picoMark_FUNCTION_BEGIN=
  33
  34 // picoChip Function Prologue : &__divmod15 = 0 bytes
  35
  36         // The picoChip instruction set has a divstep instruction which
  37         // is used to perform one iteration of a binary division algorithm.
  38         // The instruction allows 16-bit signed division to be implemented.
  39         // It does not directly allow 16-bit unsigned division to be
  40         // implemented. Thus, this function pulls out the common division
  41         // iteration for 15-bits unsigned, and then special wrappers
  42         // provide the logic to change this into a 16-bit signed or
  43         // unsigned division, as appropriate. This allows the two
  44         // versions of division to share a common implementation, reducing
  45         // code size when the two are used together. It also reduces
  46         // the maintenance overhead.
  47
  48         // Input:
  49         //      r0 - dividend
  50         //      r1 - divisor
  51         // Output:
  52         //      r0 - quotient
  53         //      r1 - remainder
  54         // R5 is unused
  55
  56         // Check for special cases. The emphasis is on detecting these as
  57         // quickly as possible, so that the main division can be started. If
  58         // the user requests division by one, division by self, and so on
  59         // then they will just have to accept that this won't be particularly
  60         // quick (relatively), whereas a real division (e.g., dividing a
  61         // large value by a small value) will run as fast as possible
  62         // (i.e., special case detection should not slow down the common case)
  63         //
  64         // Special cases to consider:
  65         //
  66         //      Division by zero.
  67         //      Division of zero.
  68         //      Inputs are equal
  69         //      Divisor is bigger than dividend
  70         //      Division by power of two (can be shifted instead).
  71         //      Division by 1 (special case of power of two division)
  72         //
  73         // Division/modulus by zero is undefined (ISO C:6.5.5), so
  74         // don't bother handling this special case.
  75         //
  76         // The special cases of division by a power of 2 are ignored, since
  77         // they cause the general case to slow down. Omitting these
  78         // special cases also reduces code size considerably.
  79
  80         // Handle divisor >= dividend separately. Note that this also handles
  81         // the case where the dividend is zero. Note that the flags must be
  82         // preserved, since they are also used at the branch destination.
  83         sub.0 r1,r0,r15
  84         sbc r0,r2 \ bge divisorGeDividend
  85 =->     sbc r1,r4
  86
  87         // Compute the shift count. The amount by which the divisor
  88         // must be shifted left to be aligned with the dividend.
  89         sub.0 r4,r2,r3
  90
  91         // Align the divisor to the dividend. Execute a divstep (since at
  92         // least one will always be executed). Skip the remaining loop
  93         // if the shift count is zero.
  94         lsl.0 r1,r3,r1 \ beq skipLoop
  95 =->     divstep r0,r1 \ add.1 r3,1,r2
  96
  97         // Execute the divstep loop until temp is 0. This assumes that the
  98         // loop count is at least one.
  99         sub.0 r3,1,r4
 100 divLoop:
 101         divstep r0,r1 \ bne divLoop
 102 =->     sub.0 r4,1,r4
 103
 104 skipLoop:
 105
 106         // The top bits of the result are the remainder. The bottom
 107         // bits are the quotient.
 108         lsr.0 r0,r2,r1 \ sub.1 16,r2,r4
 109         jr (lr ) \ lsl.0 r0,r4,r0
 110 =->     lsr.0 r0,r4,r0
 111
 112 // Special case.
 113
 114 divisorGeDividend:
 115         // The divisor is greater than or equal to the dividend. The flags
 116         // indicate which of these alternatives it is. The COPYNE can be used
 117         // to set the result appropriately, without introducing any more
 118         // branches.
 119         copy.0 r0,r1 \ copy.1 0,r0
 120         jr (lr) \ copyeq r0,r1
 121 =->     copyeq 1,r0
 122
 123 _picoMark_FUNCTION_END=
 124 // picoChip Function Epilogue : __divmod15
 125
 126
 127 //============================================================================
 128 // All DWARF information between this marker, and the END OF DWARF
 129 // marker should be included in the source file. Search for
 130 // FUNCTION_STACK_SIZE_GOES_HERE and FUNCTION NAME GOES HERE, and
 131 // provide the relevent information. Add markers called
 132 // _picoMark_FUNCTION_BEGIN and _picoMark_FUNCTION_END around the
 133 // function in question.
 134 //============================================================================
 135
 136 //============================================================================
 137 // Frame information.
 138 //============================================================================
 139
 140 .section .debug_frame
 141 _picoMark_DebugFrame=
 142
 143 // Common CIE header.
 144 .unalignedInitLong _picoMark_CieEnd-_picoMark_CieBegin
 145 _picoMark_CieBegin=
 146 .unalignedInitLong 0xffffffff
 147 .initByte 0x1   // CIE Version
 148 .ascii 16#0#    // CIE Augmentation
 149 .uleb128 0x1    // CIE Code Alignment Factor
 150 .sleb128 2      // CIE Data Alignment Factor
 151 .initByte 0xc   // CIE RA Column
 152 .initByte 0xc   // DW_CFA_def_cfa
 153 .uleb128 0xd
 154 .uleb128 0x0
 155 .align 2
 156 _picoMark_CieEnd=
 157
 158 // FDE
 159 _picoMark_LSFDE0I900821033007563=
 160 .unalignedInitLong _picoMark_FdeEnd-_picoMark_FdeBegin
 161 _picoMark_FdeBegin=
 162 .unalignedInitLong _picoMark_DebugFrame // FDE CIE offset
 163 .unalignedInitWord _picoMark_FUNCTION_BEGIN     // FDE initial location
 164 .unalignedInitWord _picoMark_FUNCTION_END-_picoMark_FUNCTION_BEGIN
 165 .initByte 0xe   // DW_CFA_def_cfa_offset
 166 .uleb128 0x0    // <-- FUNCTION_STACK_SIZE_GOES_HERE
 167 .initByte 0x4   // DW_CFA_advance_loc4
 168 .unalignedInitLong _picoMark_FUNCTION_END-_picoMark_FUNCTION_BEGIN
 169 .initByte 0xe   // DW_CFA_def_cfa_offset
 170 .uleb128 0x0
 171 .align 2
 172 _picoMark_FdeEnd=
 173
 174 //============================================================================
 175 // Abbrevation information.
 176 //============================================================================
 177
 178 .section .debug_abbrev
 179 _picoMark_ABBREVIATIONS=
 180
 181 .section .debug_abbrev
 182         .uleb128 0x1    // (abbrev code)
 183         .uleb128 0x11   // (TAG: DW_TAG_compile_unit)
 184         .initByte 0x1   // DW_children_yes
 185         .uleb128 0x10   // (DW_AT_stmt_list)
 186         .uleb128 0x6    // (DW_FORM_data4)
 187         .uleb128 0x12   // (DW_AT_high_pc)
 188         .uleb128 0x1    // (DW_FORM_addr)
 189         .uleb128 0x11   // (DW_AT_low_pc)
 190         .uleb128 0x1    // (DW_FORM_addr)
 191         .uleb128 0x25   // (DW_AT_producer)
 192         .uleb128 0x8    // (DW_FORM_string)
 193         .uleb128 0x13   // (DW_AT_language)
 194         .uleb128 0x5    // (DW_FORM_data2)
 195         .uleb128 0x3    // (DW_AT_name)
 196         .uleb128 0x8    // (DW_FORM_string)
 197 .initByte 0x0
 198 .initByte 0x0
 199
 200         .uleb128 0x2    ;# (abbrev code)
 201         .uleb128 0x2e   ;# (TAG: DW_TAG_subprogram)
 202 .initByte 0x0   ;# DW_children_no
 203         .uleb128 0x3    ;# (DW_AT_name)
 204         .uleb128 0x8    ;# (DW_FORM_string)
 205         .uleb128 0x11   ;# (DW_AT_low_pc)
 206         .uleb128 0x1    ;# (DW_FORM_addr)
 207         .uleb128 0x12   ;# (DW_AT_high_pc)
 208         .uleb128 0x1    ;# (DW_FORM_addr)
 209 .initByte 0x0
 210 .initByte 0x0
 211
 212 .initByte 0x0
 213
 214 //============================================================================
 215 // Line information. DwarfLib requires this to be present, but it can
 216 // be empty.
 217 //============================================================================
 218
 219 .section .debug_line
 220 _picoMark_LINES=
 221
 222 //============================================================================
 223 // Debug Information
 224 //============================================================================
 225 .section .debug_info
 226
 227 //Fixed header.
 228 .unalignedInitLong _picoMark_DEBUG_INFO_END-_picoMark_DEBUG_INFO_BEGIN
 229 _picoMark_DEBUG_INFO_BEGIN=
 230 .unalignedInitWord 0x2
 231 .unalignedInitLong _picoMark_ABBREVIATIONS
 232 .initByte 0x2
 233
 234 // Compile unit information.
 235 .uleb128 0x1    // (DIE 0xb) DW_TAG_compile_unit)
 236 .unalignedInitLong _picoMark_LINES
 237 .unalignedInitWord _picoMark_FUNCTION_END
 238 .unalignedInitWord _picoMark_FUNCTION_BEGIN
 239 // Producer is `picoChip'
 240 .ascii 16#70# 16#69# 16#63# 16#6f# 16#43# 16#68# 16#69# 16#70# 16#00#
 241 .unalignedInitWord 0xcafe // ASM language
 242 .ascii 16#0# // Name. DwarfLib expects this to be present.
 243
 244 .uleb128 0x2    ;# (DIE DW_TAG_subprogram)
 245
 246 // FUNCTION NAME GOES HERE. Use `echo name | od -t x1' to get the hex. Each hex
 247 // digit is specified using the format 16#XX#
 248 .ascii 16#5f# 16#64# 16#69# 16#76# 16#6d# 16#6f# 16#64# 16#31# 16#35# 16#0# // Function name `_divmod15'
 249 .unalignedInitWord _picoMark_FUNCTION_BEGIN     // DW_AT_low_pc
 250 .unalignedInitWord _picoMark_FUNCTION_END       // DW_AT_high_pc
 251
 252 .initByte 0x0   // end of compile unit children.
 253
 254 _picoMark_DEBUG_INFO_END=
 255
 256 //============================================================================
 257 // END OF DWARF
 258 //============================================================================
 259
 260 .section .endFile
 261 // End of picoChip ASM file