use core::intrinsics;

// NOTE This function and the ones below are implemented using assembly because they using a custom
// calling convention which can't be implemented using a normal Rust function.
// NOTE The only difference between the iOS and non-iOS versions of those functions is that the iOS
// versions use 3 leading underscores in the names of called functions instead of 2.
#[cfg(not(any(target_os = "ios", target_env = "msvc")))]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_uidivmod() {
    llvm_asm!("
        push {lr}
        sub sp, sp, #4
        mov r2, sp
        bl __udivmodsi4
        ldr r1, [sp]
        add sp, sp, #4
        pop {pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(target_os = "ios")]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_uidivmod() {
    llvm_asm!("
        push {lr}
        sub sp, sp, #4
        mov r2, sp
        bl ___udivmodsi4
        ldr r1, [sp]
        add sp, sp, #4
        pop {pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(not(target_os = "ios"))]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_uldivmod() {
    llvm_asm!("
        push {r4, lr}
        sub sp, sp, #16
        add r4, sp, #8
        str r4, [sp]
        bl __udivmoddi4
        ldr r2, [sp, #8]
        ldr r3, [sp, #12]
        add sp, sp, #16
        pop {r4, pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(target_os = "ios")]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_uldivmod() {
    llvm_asm!("
        push {r4, lr}
        sub sp, sp, #16
        add r4, sp, #8
        str r4, [sp]
        bl ___udivmoddi4
        ldr r2, [sp, #8]
        ldr r3, [sp, #12]
        add sp, sp, #16
        pop {r4, pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(not(target_os = "ios"))]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_idivmod() {
    llvm_asm!("
        push {r0, r1, r4, lr}
        bl __aeabi_idiv
        pop {r1, r2}
        muls r2, r2, r0
        subs r1, r1, r2
        pop {r4, pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(target_os = "ios")]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_idivmod() {
    llvm_asm!("
        push {r0, r1, r4, lr}
        bl ___aeabi_idiv
        pop {r1, r2}
        muls r2, r2, r0
        subs r1, r1, r2
        pop {r4, pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(not(target_os = "ios"))]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_ldivmod() {
    llvm_asm!("
        push {r4, lr}
        sub sp, sp, #16
        add r4, sp, #8
        str r4, [sp]
        bl __divmoddi4
        ldr r2, [sp, #8]
        ldr r3, [sp, #12]
        add sp, sp, #16
        pop {r4, pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

#[cfg(target_os = "ios")]
#[naked]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
pub unsafe fn __aeabi_ldivmod() {
    llvm_asm!("
        push {r4, lr}
        sub sp, sp, #16
        add r4, sp, #8
        str r4, [sp]
        bl ___divmoddi4
        ldr r2, [sp, #8]
        ldr r3, [sp, #12]
        add sp, sp, #16
        pop {r4, pc}
    " ::: "memory" : "volatile");
    intrinsics::unreachable();
}

// FIXME: The `*4` and `*8` variants should be defined as aliases.
extern "C" {
    // optimized memcpy using assembly
    fn memcpy(dest: *mut u8, src: *const u8, n: usize);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memcpy(dest: *mut u8, src: *const u8, n: usize) {
    memcpy(dest, src, n);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memcpy4(dest: *mut u8, src: *const u8, n: usize) {
    // We are guaranteed 4-alignment, so accessing at u32 is okay.
    // let mut dest = dest as *mut u32;
    // let mut src = src as *mut u32;

    // while n >= 4 {
    //     *dest = *src;
    //     dest = dest.offset(1);
    //     src = src.offset(1);
    //     n -= 4;
    // }

    __aeabi_memcpy(dest as *mut u8, src as *const u8, n);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memcpy8(dest: *mut u8, src: *const u8, n: usize) {
    __aeabi_memcpy4(dest, src, n);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memmove(dest: *mut u8, src: *const u8, n: usize) {
    ::mem::memmove(dest, src, n);
}

#[cfg(not(any(target_os = "ios", target_env = "msvc")))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memmove4(dest: *mut u8, src: *const u8, n: usize) {
    __aeabi_memmove(dest, src, n);
}

#[cfg(not(any(target_os = "ios", target_env = "msvc")))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memmove8(dest: *mut u8, src: *const u8, n: usize) {
    __aeabi_memmove(dest, src, n);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memset(dest: *mut u8, n: usize, c: i32) {
    // Note the different argument order
    ::mem::memset(dest, c, n);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memset4(dest: *mut u8, mut n: usize, c: i32) {
    let mut dest = dest as *mut u32;

    let byte = (c as u32) & 0xff;
    let c = (byte << 24) | (byte << 16) | (byte << 8) | byte;

    while n >= 4 {
        *dest = c;
        dest = dest.offset(1);
        n -= 4;
    }

    __aeabi_memset(dest as *mut u8, n, byte as i32);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memset8(dest: *mut u8, n: usize, c: i32) {
    __aeabi_memset4(dest, n, c);
}

#[cfg(not(target_os = "ios"))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memclr(dest: *mut u8, n: usize) {
    __aeabi_memset(dest, n, 0);
}

#[cfg(not(any(target_os = "ios", target_env = "msvc")))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memclr4(dest: *mut u8, n: usize) {
    __aeabi_memset4(dest, n, 0);
}

#[cfg(not(any(target_os = "ios", target_env = "msvc")))]
#[cfg_attr(not(feature = "mangled-names"), no_mangle)]
#[cfg_attr(thumb, linkage = "weak")]
pub unsafe extern "aapcs" fn __aeabi_memclr8(dest: *mut u8, n: usize) {
    __aeabi_memset4(dest, n, 0);
}