runtime: move start of libc into separate folder
Anton Lydike
1 year ago
parent
a28bf834ac
commit
1bd754953c
@ -1,152 +0,0 @@
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; string operations in RISC-V Assembly
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; All function restore all registers after use (even caller-saved ones)
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.global NULL
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; A global constant, points to the empty string
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.global strlen
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; size_t libstr_strlen(char* str)
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; return the length of str
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.global strncpy
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; char *strncpy(char *dest, const char *src, size_t n)
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; copy n bytes from source into dest. If source ends before n bytes, the rest is filled with null-bytes
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; returns pointer to dest
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.global strcpy
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; char *strncpy(char *dest, const char *src)
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; copy string src into dest, including null terminator
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; returns pointer to dest
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.global memchr
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; void *memchr(const void *str, char c, size_t n)
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; search vor the first occurance of c in str
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; returns a pointer to the first occurance, or NULL
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.global memset
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; void *memset(void *str, char c, size_t n)
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; copies the character c to the first n characters of str.
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;.global memcmp
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;.global memcpy
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;.global strcat
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; Create NullPtr constant
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.set NULL, 0x00
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.text
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strlen:
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; size_t strlen(char* str)
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; push s1, s2 to the stack
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sw s1, sp, -4
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sw s2, sp, -8
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; since no subroutines are called, we don't need to increment or decrement the sp
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addi s2, zero, -1 ; length (since null byte is counted by this method, we return len - 1)
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__strlen_loop:
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lb s1, a0, 0 ; read character
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addi s2, s2, 1 ; increment number bytes read
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addi a0, a0, 1
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bne s1, zero, __strlen_loop
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; we are done, set return value in a0
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add a0, zero, s2
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; pop s1, s2, from stack
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lw s1, sp, -4
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lw s2, sp, -8
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ret
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strncpy:
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; char *strncpy(char *dest, const char *src, size_t n)
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; copy size bytes from source to dest
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sw s1, sp, -4 ; push s1 to the stack
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sw s2, sp, -8 ; push s1 to the stack
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add s1, a0, zero ; save dest pointer for return
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__strncpy_loop:
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beq a2, zero, __strncpy_end
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; copy byte
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lb s2, a1, 0 ; read first byte from src
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sb s2, a0, 0 ; write first byte to dest
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; increment pointers
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addi a0, a0, 1
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addi a1, a1, 1
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; one less byte to copy
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addi a2, a2, -1
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; if we read the terminating byte, jump to fill code
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beq s2, zero, __strncpy_fill
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; otherwise continue copying
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j __strncpy_loop
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__strncpy_fill:
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; fill remaining space with 0 bytes
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; if no bytes left, stop filling
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beq a2, zero, __strncpy_end
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sb zero, a0, 0
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addi a0, a0, 1
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addi a2, a2, -1
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j __strncpy_fill
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__strncpy_end:
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; set return value
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add a0, zero, s1
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; pop s1, s2 from stack
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lw s1, sp, -4
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lw s2, sp, -8
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ret
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strcpy:
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; char *strncpy(char *dest, const char *src)
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sw s1, sp, -4 ; push s1 to the stack
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sw s2, sp, -8 ; push s1 to the stack
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add s1, a0, zero ; save dest pointer for return
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__strcpy_loop:
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; copy byte
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lb s2, a1, 0 ; read first byte from src
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sb s2, a0, 0 ; write first byte to dest
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; increment pointers
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addi a0, a0, 1
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addi a1, a1, 1
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bne s2, zero, __strcpy_loop
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; we are done copying, return
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; set return value
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add a0, zero, s1
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; pop s1, s2 from stack
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lw s1, sp, -4
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lw s2, sp, -8
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ret
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memchr:
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; void *memchr(const void *str, char c, size_t n)
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sw s1, sp, -4 ; push s1 to the stack
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__memchr_loop:
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beq a2, zero, __memchr_ret_null
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lb s1, a0, 0
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addi a0, a0, 1 ; let a0 point to the next byte
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addi a2, a2, -1 ; decrement bytes to copy by 1
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bne s1, s2, __memchr_loop
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; return pointer to prev byte (as the prev byte actually matched a1)
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addi a0, a0, -1
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; pop s1, s2 from stack
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lw s1, sp, -4
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ret
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__memchr_ret_null:
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; nothing found, return nullptr
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addi a0, zero, NULL
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lw s1, sp, -4
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ret
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memset:
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; void *memset(void *str, char c, size_t n)
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__memset_loop:
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beq a2, zero, __memset_ret
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sb a1, a0, 0
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addi a0, a0, 1
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addi a2, a2, -1
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j __memset_loop
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__memset_ret:
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ret
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@ -0,0 +1,31 @@
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# RiscEmu LibC
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This is a very basic implementation of libc in risc-v assembly, meant specifically for the riscemu emulator.
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This is currently very incomplete, only a handful of methods are implemented, and most of them pretty basic.
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## Contents:
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### `stdlib.s`
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Basic implementations of:
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- `malloc`/`free` (that leaks memory)
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- `rand`/`srand` (using xorshift)
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- `exit`/`atexit` (supporting up to 8 exit handlers)
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### `string.s`
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Somewhat nice implementations of:
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- `strlen`
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- `strncpy`
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- `strcpy`
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- `memchr`
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- `memset` (very basic byte-by-byte copy)
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## Correctness:
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This library is 100% untested. Feel free to report bugs using github issues. I'm sure ther are many. We are working on testing!
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@ -0,0 +1,154 @@
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// string operations in RISC-V Assembly
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//
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// Copyright (c) 2023 Anton Lydike
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// SPDX-License-Identifier: MIT
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.global NULL
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// A global constant representing zero
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.global strlen
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// size_t libstr_strlen(char* str)
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// return the length of str
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.global strncpy
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// char *strncpy(char *dest, const char *src, size_t n)
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// copy n bytes from source into dest. If source ends before n bytes, the rest is filled with null-bytes
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// returns pointer to dest
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.global strcpy
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// char *strncpy(char *dest, const char *src)
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// copy string src into dest, including null terminator
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// returns pointer to dest
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.global memchr
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// void *memchr(const void *str, char c, size_t n)
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// search vor the first occurance of c in str
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// returns a pointer to the first occurance, or NULL
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.global memset
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// void *memset(void *str, char c, size_t n)
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// copies the character c to the first n characters of str.
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//.global memcmp
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//.global memcpy
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//.global strcat
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// Create NullPtr constant
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.set NULL, 0x00
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.text
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strlen:
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// size_t strlen(char* str)
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// push s1, s2 to the stack
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sw s1, sp, -4
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sw s2, sp, -8
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// since no subroutines are called, we don't need to increment or decrement the sp
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addi s2, zero, -1 // length (since null byte is counted by this method, we return len - 1)
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__strlen_loop:
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lb s1, a0, 0 // read character
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addi s2, s2, 1 // increment number bytes read
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addi a0, a0, 1
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bne s1, zero, __strlen_loop
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// we are done, set return value in a0
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add a0, zero, s2
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// pop s1, s2, from stack
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lw s1, sp, -4
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lw s2, sp, -8
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ret
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strncpy:
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// char *strncpy(char *dest, const char *src, size_t n)
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// copy size bytes from source to dest
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sw s1, sp, -4 // push s1 to the stack
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sw s2, sp, -8 // push s1 to the stack
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add s1, a0, zero // save dest pointer for return
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__strncpy_loop:
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beq a2, zero, __strncpy_end
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// copy byte
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lb s2, a1, 0 // read first byte from src
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sb s2, a0, 0 // write first byte to dest
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// increment pointers
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addi a0, a0, 1
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addi a1, a1, 1
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// one less byte to copy
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addi a2, a2, -1
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// if we read the terminating byte, jump to fill code
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beq s2, zero, __strncpy_fill
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// otherwise continue copying
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j __strncpy_loop
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__strncpy_fill:
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// fill remaining space with 0 bytes
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// if no bytes left, stop filling
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beq a2, zero, __strncpy_end
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sb zero, a0, 0
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addi a0, a0, 1
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addi a2, a2, -1
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j __strncpy_fill
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__strncpy_end:
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// set return value
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add a0, zero, s1
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// pop s1, s2 from stack
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lw s1, sp, -4
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lw s2, sp, -8
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ret
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strcpy:
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// char *strncpy(char *dest, const char *src)
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sw s1, sp, -4 // push s1 to the stack
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sw s2, sp, -8 // push s1 to the stack
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add s1, a0, zero // save dest pointer for return
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__strcpy_loop:
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// copy byte
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lb s2, a1, 0 // read first byte from src
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sb s2, a0, 0 // write first byte to dest
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// increment pointers
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addi a0, a0, 1
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addi a1, a1, 1
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bne s2, zero, __strcpy_loop
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// we are done copying, return
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// set return value
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add a0, zero, s1
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// pop s1, s2 from stack
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lw s1, sp, -4
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lw s2, sp, -8
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ret
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memchr:
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// void *memchr(const void *str, char c, size_t n)
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sw s1, sp, -4 // push s1 to the stack
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__memchr_loop:
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beq a2, zero, __memchr_ret_null
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lb s1, a0, 0
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addi a0, a0, 1 // let a0 point to the next byte
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addi a2, a2, -1 // decrement bytes to copy by 1
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bne s1, s2, __memchr_loop
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// return pointer to prev byte (as the prev byte actually matched a1)
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addi a0, a0, -1
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// pop s1, s2 from stack
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lw s1, sp, -4
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ret
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__memchr_ret_null:
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// nothing found, return nullptr
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addi a0, zero, NULL
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lw s1, sp, -4
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ret
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memset:
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// void *memset(void *str, char c, size_t n)
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__memset_loop:
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beq a2, zero, __memset_ret
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sb a1, a0, 0
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addi a0, a0, 1
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addi a2, a2, -1
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j __memset_loop
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__memset_ret:
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ret
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