FreeBSD/Linux Kernel Cross Reference
sys/libkern/arm/ldivmod.S

     /*
      * Copyright (C) 2012 Andrew Turner
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     */
    
    #include <machine/asm.h>
    __FBSDID("$FreeBSD: releng/11.0/sys/libkern/arm/ldivmod.S 285338 2015-07-09 21:02:40Z andrew $");
    
    /*
     * These calculate:
     * q = n / m 
     * With a remainer r.
     *
     * They take n in {r0, r1} and m in {r2, r3} then pass them into the
     * helper function. The hepler functions return q in {r0, r1} as
     * required by the API spec however r is returned on the stack. The
     * ABI required us to return r in {r2, r3}.
     *
     * We need to allocate 8 bytes on the stack to store r, the link
     * register, and a pointer to the space where the helper function
     * will write r to. After returning from the helper fuinction we load
     * the old link register and r from the stack and return.
     */
    ENTRY_NP(__aeabi_ldivmod)
            sub     sp, sp, #8      /* Space for the remainder */
            stmfd   sp!, {sp, lr}   /* Save a pointer to the above space and lr */
            bl      PIC_SYM(_C_LABEL(__kern_ldivmod), PLT)
            ldr     lr, [sp, #4]    /* Restore lr */
            add     sp, sp, #8      /* Move sp to the remainder value */
            ldmfd   sp!, {r2, r3}   /* Load the remainder */
            RET
    END(__aeabi_ldivmod)
    
    ENTRY_NP(__aeabi_uldivmod)
            sub     sp, sp, #8      /* Space for the remainder */
            stmfd   sp!, {sp, lr}   /* Save a pointer to the above space and lr */
            bl      PIC_SYM(_C_LABEL(__qdivrem), PLT)
            ldr     lr, [sp, #4]    /* Restore lr */
            add     sp, sp, #8      /* Move sp to the remainder value */
            ldmfd   sp!, {r2, r3}   /* Load the remainder */
            RET
    END(__aeabi_uldivmod)

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