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To build a generic swap in C, pass the size explicitly, create a temporary byte buffer, then use memcpy three times to rotate the bit patterns. VLA char buffer[size] is a GCC thing, for a more portable version malloc the temp and free it. Stanford CS107, lecture 4

tetsuo

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45,838 次观看 • 27 天前 •via X (Twitter)

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You cannot add to a void pointer in C. The compiler does not know the size. The everyday fix is to cast it to char* so the math is in bytes, then multiply by the element size yourself. Stanford CS107, lecture 4

You cannot add to a void pointer in C. The compiler does not know the size. The everyday fix is to cast it to char* so the math is in bytes, then multiply by the element size yourself. Stanford CS107, lecture 4

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In C, `array[i]` does not add i to the address. It adds i times the size of one element. Assembly has to do that multiply. C hides it. Stanford CS107, lecture 9.

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** Sega Genesis 3D engine update 4 ** Never can leave a good rabbit hole undug ! .. updates since last update : Changed frame buffer from a VDP tile friendly buffer to a linear buffer which needs CPU translation , which speedup drawing a LOT not having to worry about tile boundaries albiet slows buffer sending to VRAM. The interior filling of triangles now is running at 1.5c ( 68k cycles ) per pixel ! however sending the buffer is twice as slow per byte as we need the CPU to send the buffer to VRAM to write to the tile format the VDP needs, rather than DMA directly to VRAM . Overall speedup 25% + as the drawing speedup is much greater than the frame buffer slow down. Optimised Line drawing and Triangle filling -near optimal now for the linear frame buffer. Triangle drawing might get a little bit more yet. Quad drawing is next on the list as that will speedup drawing quads. Some gains will come from been smart about partial clearing of RAM buffers and partial sending to VRAM buffers, rather than send the whole buffer. Vertice rotation and projection needs a lot of optimising .. i expect good gains to come from this - this is all in C at present and all calced in real time. Line and Triangle drawing are in assembly but all vertex manipulation is in C. #SGDK #MegaDrive #SegaGenesis

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This is a common C bug. You write a MAX macro, then call MAX(m++, n++). The preprocessor pastes the text, so it becomes (m++ > n++) ? m++ : n++. The smaller one increments once. The larger one increments twice. Stanford CS107, lecture 12

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