[avr-gcc-list] odd behaviour with type casting

[Paul Thomas]

I'm getting very wrong math in one instance using a casting,  negative
numbers and a division. If I don't do any 1 of those three things it
works fine. This is with an atxmega32a4 using both the atmel avr-gcc
4.5.1 (avr-gcc (AVR_8_bit_GNU_Toolchain_3.2.3_314) 4.5.1) as well as
4.5.1 gcc built with the script from AvrFreaks. The code snippet to
demonstrate this is:

    int16_t var1_16, var2_16, var3_16;
    int32_t var1_32, var2_32;

    var1_16 = pcpv_data->board.vout;
    var2_16 = -48;
    var3_16 = ((int32_t)var1_16 * (int32_t)var2_16) / 10;
    printf("WRONG: using casting                        : %d = ( %d *
%d) / 10\n",var3_16, var1_16, var2_16);

    var1_16 = -pcpv_data->board.vout;
    var2_16 = 48;
    var3_16 = ((int32_t)var1_16 * (int32_t)var2_16) / 10;
    printf("RIGHT: using casting, positive vars         : %d = ( %d *
%d) / 10\n",var3_16, var1_16, var2_16);

    var1_16 = pcpv_data->board.vout;
    var2_16 = -48;
    var3_16 = ((int32_t)var1_16 * (int32_t)var2_16);
    printf("RIGHT: using casting, without the division  : %d = ( %d *
%d)\n",var3_16, var1_16, var2_16);

    var1_16 = -32;
    var2_16 = -48;
    var3_16 = ((int32_t)var1_16 * (int32_t)var2_16) / 10;
    printf("RIGHT: using casting, assigned from constant: %d = ( %d *
%d) / 10\n",var3_16, var1_16, var2_16);

    var1_32 = pcpv_data->board.vout;
    var2_32 = -48;
    var3_16 = (var1_32 * var2_32) / 10;
    printf("RIGHT: using int32_t vars                   : %d = ( %ld *
%ld) / 10\n",var3_16, var1_32, var2_32);

With a result of this:

WRONG: using casting                        : 13260 = ( -32 * -48) / 10
RIGHT: using casting, positive vars         : 153 = ( 32 * 48) / 10
RIGHT: using casting, without the division  : 1536 = ( -32 * -48)
RIGHT: using casting, assigned from constant: 153 = ( -32 * -48) / 10
RIGHT: using int32_t vars                   : 153 = ( -32 * -48) / 10

A section of the .lst file is here:
http://pastebin.com/AMX2Mr75

thanks,
Paul