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added description of control flow behavior (wrote this text at 34C3, not sure why I didn't post it at the time, it would be good if someone could independently verify it all)
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1.0 can be multiplied 63 times by 0.5 until the result compares equal zero. This is consistent with a 7-bit exponent and output subnormal flushing.
1.0 can be multiplied 63 times by 0.5 until the result compares equal zero. This is consistent with a 7-bit exponent and output subnormal flushing.
+
+== Control Flow ==
+
+Control flow is implemented using three independent stacks: an 8-deep IF stack, a 4-deep CALL stack, and a 4-deep LOOP stack. All stacks are initially empty. After every instruction, the stacks are checked in the order CALL->IF->LOOP and if a stack is popped, the program counter update overwrites any previous update, even if set by a JMP instruction. The IF/LOOP stacks can only pop one entry per instruction, whereas the CALL stack can be completely emptied. If the CALL stack is popped four times in a single instruction, the last program counter update is missed. Executing a BREAK on an empty LOOP stack hangs the GPU. The stacks are actually ring buffers: overflow overwrites the oldest entry, the stack size is clamped.