porting over pcboot codebase

[com32] / src / libc / string_s.asm

diff --git a/src/libc/string_s.asm b/src/libc/string_s.asm
new file mode 100644 (file)
index 0000000..4545d16
--- /dev/null
+++ b/src/libc/string_s.asm
@@ -0,0 +1,174 @@
+; pcboot - bootable PC demo/game kernel
+; Copyright (C) 2018  John Tsiombikas <nuclear@member.fsf.org>
+; 
+; This program 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 of the License, or
+; (at your option) any later version.
+; 
+; This program 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.
+; 
+; You should have received a copy of the GNU General Public License
+; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+       ; standard C memset
+       global memset
+memset:
+       push ebp
+       mov ebp, esp
+       push edi
+
+       mov edi, [ebp + 8]
+       push edi
+       mov al, [ebp + 12]
+       mov ah, al
+       mov cx, ax
+       shl eax, 16
+       mov ax, cx
+       mov ecx, [ebp + 16]
+
+       test ecx, ecx
+       jz .done
+
+       ; write 1, 2, or 3 times until we reache a 32bit-aligned dest address
+       mov edx, edi
+       and edx, 3
+       jz .main
+       jmp [.pre_tab + ecx * 4]
+
+.pre_tab dd .main, .pre1, .pre2, .pre3
+.pre3: stosb
+       dec ecx
+.pre2: stosb
+       dec ecx
+.pre1: stosb
+       dec ecx
+       jz .done
+
+       ; edi is 32bit-aligned here, write ecx>>2 32bit values
+.main:
+       push ecx
+       shr ecx, 2
+       rep stosd
+       pop ecx
+
+       ; write any trailing bytes
+       and ecx, 3
+       jmp [.post_tab + ecx * 4]
+
+.post_tab dd .done, .post1, .post2, .post3
+.post3:        stosb
+.post2:        stosb
+.post1:        stosb
+
+.done: pop eax
+       pop edi
+       pop ebp
+       ret
+
+
+       ; same as memset but copies 16bit values, and the count is the number
+       ; of 16bit values to copy, not bytes.
+       global memset16
+memset16:
+       push ebp
+       mov ebp, esp
+       push edi
+
+       mov edi, [ebp + 8]
+       push edi
+       mov ax, [ebp + 12]
+       shl eax, 16
+       mov ax, [ebp + 12]
+       mov ecx, [ebp + 16]
+
+       test ecx, ecx
+       jz .done
+
+       mov edx, edi
+       and edx, 3
+       jz .main
+       jmp [.pre_tab + edx * 4]
+
+.pre_tab dd .main, .pre1, .pre2, .pre3
+.pre3:
+       ; unaligned by +3:
+       ; same as next one, but jump to ms16main instead of falling through
+       mov [edi], al
+       mov [edi + ecx * 2 - 1], ah
+       rol eax, 8
+       inc edi
+       dec ecx
+       jz .done
+       jmp .main
+.pre1:
+       ; unaligned by +1:
+       ; - write low byte at edi
+       ; - write high byte at the end
+       ; - rotate by 8 for the rest
+       ; - decrement ecx
+       mov [edi], al
+       mov [edi + ecx * 2 - 1], ah
+       rol eax, 8
+       inc edi
+       dec ecx
+       jz .done
+.pre2:
+       ; unaligned by +2
+       stosw
+       dec ecx
+       jz .done
+
+.main:
+       push ecx
+       shr ecx, 1
+       rep stosd
+       pop ecx
+
+       and ecx, 1
+       jz .done
+       stosw
+.done:
+       pop eax
+       pop edi
+       pop ebp
+       ret
+
+
+       ; standard C memcpy
+       global memcpy
+memcpy:
+       push ebp
+       mov ebp, esp
+       push edi
+       push esi
+
+       mov edi, [ebp + 8]
+       mov esi, [ebp + 12]
+       mov ecx, [ebp + 16]
+
+       test ecx, ecx
+       jz .done
+
+       mov edx, ecx
+       shr ecx, 2
+       rep movsd
+
+       and edx, 3
+       jmp [.post_tab + edx * 4]
+
+.post_tab dd .done, .post1, .post2, .post3
+.post3:        movsb
+.post2:        movsb
+.post1:        movsb
+
+.done:
+       pop esi
+       pop edi
+       pop ebp
+       ret
+
+; vi:set ts=8 sts=8 sw=8 ft=nasm: