qmul8()

LIB8STATIC_ALWAYS_INLINE uint8_t qmul8	(	uint8_t	i,
		uint8_t	j )

8x8 bit multiplication with 8-bit result, saturating at 0xFF.

Parameters

i	first byte to multiply
j	second byte to multiply

Returns

the product of i * j, capping at 0xFF

Definition at line 486 of file math8.h.

                                                             {
#if QMUL8_C == 1
    unsigned p = (unsigned)i * (unsigned)j;
    if (p > 255)
        p = 255;
    return p;
#elif QMUL8_AVRASM == 1
    asm volatile(
        /* Multiply 8-bit i * 8-bit j, giving 16-bit r1,r0 */
        "  mul %0, %1          \n\t"
        /* Extract the LOW 8-bits (r0) */
        "  mov %0, r0          \n\t"
        /* If high byte of result is zero, all is well. */
        "  tst r1              \n\t"
        "  breq Lnospill_%=    \n\t"
        /* If high byte of result > 0, saturate to 0xFF */
        "  ldi %0, 0xFF         \n\t"
        "Lnospill_%=:          \n\t"
        /* Restore r1 to "0"; it's expected to always be that */
        "  clr __zero_reg__    \n\t"
        : "+d"(i) // r16-r31, restricted by ldi
        : "r"(j)
        : "r0", "r1");
    return i;
#else
#error "No implementation for qmul8 available."
#endif
}

References LIB8STATIC_ALWAYS_INLINE.

Referenced by operator*().

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