[Bug target/50281] result registers are overwritten giving incorrect result

[NickParker at Eaton dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50281

--- Comment #5 from NickParker at Eaton dot com 2011-09-03 01:32:20 UTC ---
Sorry. I pasted a broken version. Before. Code below works.


uint32_t MulU3U3S3(uint32_t a_u4, uint32_t b_u4)
{
    //uint32_t answer;

    asm volatile
    (

        "push r0"                  "\n\t"
        "push r1"                  "\n\t"
        "push r10"                 "\n\t"

        "clr r10"                  "\n\t"      // zero register

        // 0 byte shifts
        "mul %A1,%A2"              "\n\t"      // a1a2
        "mov r2,r0"                "\n\t"
        "mov r3,r1"                "\n\t"

        // 1 byte shifts
        "mul %A1,%B2"              "\n\t"
        "add r3,r0"                "\n\t"
        "adc r4,r1"                "\n\t"
        "adc r5,r10"               "\n\t"

        "mul %A2,%B1"              "\n\t"
        "add r3,r0"                "\n\t"
        "adc r4,r1"                "\n\t"
        "adc r5,r10"               "\n\t"

        // 2 byte shifts
        "mul %A1,%C2"              "\n\t"
        "add r4,r0"                "\n\t"
        "adc r5,r1"                "\n\t"
        "adc r6,r10"               "\n\t"

        "mul %A2,%C1"              "\n\t"
        "add r4,r0"                "\n\t"
        "adc r5,r1"                "\n\t"
        "adc r6,r10"               "\n\t"

        "mul %B2,%B1"              "\n\t"
        "add r4,r0"                "\n\t"
        "adc r5,r1"                "\n\t"
        "adc r6,r10"               "\n\t"

        // 3 byte shifts
        "mul %B1,%C2"              "\n\t"
        "add r5,r0"                "\n\t"
        "adc r6,r1"                "\n\t"
        "adc r7,r10"               "\n\t"

        "mul %B2,%C1"              "\n\t"
        "add r5,r0"                "\n\t"
        "adc r6,r1"                "\n\t"
        "adc r7,r10"               "\n\t"

        // 4 byte shifts
        "mul %C2,%C1"              "\n\t"
        "add r6,r0"                "\n\t"
        "adc r7,r1"                "\n\t"

        "mov %A0,r5"               "\n\t"
        "mov %B0,r6"               "\n\t"
        "mov %C0,r7"               "\n\t"
        "clr %D0"                  "\n\t"

        //"adc %G0,r20"              "\n\t"
        "pop r10"                  "\n\t"
        "pop r1"                   "\n\t"
        "pop r0"                   "\n\t"

    : "=&r" (answer)
    : "r" (a_u4), "r" (b_u4)
    : "r2","r3","r4","r5","r6","r7","r10"
    );

    return (answer);
}