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Comment by dudu24

2 hours ago

If you have a ruler and it goes to 12 inches, you should normalize by the length L and not by 13, the number of points on the ruler.

10 comments

dudu24

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lacedeconstruct  1 hour ago

yes but >> 8 is so much faster

  • xigoi  12 minutes ago

    You don’t divide a float by 256 by shifting it right eight bits; that would yield complete garbage. You subtract 8 from the exponent, then check if you got an underflow.

  • dist-epoch  1 hour ago

    Only in micro-benchmarks.

    For real usage, today's CPUs are limited by memory bandwidth.

    • lacedeconstruct  35 minutes ago

      What are you talking about in a hot loop in my software renderer this is like 10x faster

          // color4_t result = {
    //     .r = (src.r * src.a + dst.r * inv_alpha) * INV_255,
    //     .g = (src.g * src.a + dst.g * inv_alpha) * INV_255,
    //     .b = (src.b * src.a + dst.b * inv_alpha) * INV_255,
    //     .a = src.a + (dst.a * inv_alpha) * INV_255
    // };

    // 1/256 but much faster
    color4_t result = {
        .r = (src.r * src.a + dst.r * inv_alpha) >> 8,
        .g = (src.g * src.a + dst.g * inv_alpha) >> 8,
        .b = (src.b * src.a + dst.b * inv_alpha) >> 8,
        .a = src.a + ((dst.a * inv_alpha) >> 8)
    };

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