nscale8_LEAVING_R1_DIRTY()

LIB8STATIC_ALWAYS_INLINE void nscale8_LEAVING_R1_DIRTY	(	uint8_t &	i,
		fract8	scale )

In place modifying version of scale8() that does not clean up the R1 register on AVR.

If you are doing several "scale8()'s" in a row, use this, and then explicitly call cleanup_R1().

Warning

You MUST call cleanup_R1() after using this function!

Warning

This function always modifies its arguments in place!

Parameters

i	input value to scale
scale	scale factor, in n/256 units

See also

scale8()

Definition at line 223 of file scale8.h.

                                                                     {
#if SCALE8_C == 1
#if (FASTLED_SCALE8_FIXED == 1)
    i = (((uint16_t)i) * ((uint16_t)(scale) + 1)) >> 8;
#else
    i = ((int)i * (int)(scale)) >> 8;
#endif
#elif SCALE8_AVRASM == 1
    asm volatile(
#if (FASTLED_SCALE8_FIXED == 1)
        // Multiply 8-bit i * 8-bit scale, giving 16-bit r1,r0
        "mul %0, %1          \n\t"
        // Add i to r0, possibly setting the carry flag
        "add r0, %0         \n\t"
        // load the immediate 0 into i (note, this does _not_ touch any flags)
        "ldi %0, 0x00       \n\t"
        // walk and chew gum at the same time
        "adc %0, r1          \n\t"
#else
        /* Multiply 8-bit i * 8-bit scale, giving 16-bit r1,r0 */
        "mul %0, %1    \n\t"
        /* Move the high 8-bits of the product (r1) back to i */
        "mov %0, r1    \n\t"
#endif
        /* R1 IS LEFT DIRTY HERE; YOU MUST ZERO IT OUT YOURSELF */
        /* "clr __zero_reg__    \n\t" */
 
        : "+d"(i)    /* writes to i; r16-r31, restricted by ldi */
        : "r"(scale) /* uses scale */
        : "r0", "r1" /* clobbers r0, r1 */
    );
#else
#error "No implementation for nscale8_LEAVING_R1_DIRTY available."
#endif
}

References LIB8STATIC_ALWAYS_INLINE, and scale.