61 lines
2.0 KiB
C++
61 lines
2.0 KiB
C++
#include "mtl/target.hpp"
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#include "mtl/fixed.hpp"
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TARGET_ARM_MODE
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namespace mtl {
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fixed fixed::operator/(fixed rhs) const noexcept {
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int32_t raw_result;
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asm(
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// This division implementation has two methods it can use.
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// The fastest uses a left shift followed by a single division. The value is shifted
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// first to preserve the decimal part. Unfortunately, this means large numerators
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// will cause the operation to overflow. In this case, a compatible method will be
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// used. This method uses two divisions, one to calculate the integral quotient,
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// and one to calculate the decimal part. Both these methods work for negative numbers as well.
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".arm;"
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"movs r1, %[d];" // Load numerator and denominator, and check if negative or zero
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"beq 4f;"
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"movs r0, %[n];"
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"blt 1f;"
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"tst r0, #0x7e000000;" // Check if the numerator is large enough to overflow
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"bne 3f;"
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"b 2f;"
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"1:" // check_negative
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"mvn r2, r0;" // Check if the numerator is large enough to overflow.
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"tst r2, #0x7e000000;"
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"bne 3f;"
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"2:" // fast_div // Fast method
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"lsl r0, #6;" // Shift first to avoid truncation
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"swi #0x60000;" // GBA Div syscall
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"mov %[res], r0;"
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"b 5f;"
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"3:" // compat_div // Compatible method
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"swi #0x60000;" // Compute quotient and shift
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"lsl r2, r0, #6;"
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"mov r0, r1;" // Div syscall puts the modulus in r1, use it as the numerator
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"lsr r1, %[d], #6;" // Load the denominator again, shifted right to calculate decimal part
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"swi #0x60000;"
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"mov %[res], r2;" // Calculate the final result
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"add %[res], r0;"
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"b 5f;"
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"4:" // zero_div
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"teq %[n], %[d];" // Set result to largest possible negative/positive value.
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"movmi %[res], #0x80000000;"
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"movpl %[res], #0x7FFFFFFF;"
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"5:"
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: [res] "=r" (raw_result)
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: [n] "r" (x),
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[d] "r" (rhs.x)
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: "r0", "r1", "r2", "r3"
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);
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return from_raw(raw_result);
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}
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} // namespace mtl
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TARGET_END_MODE
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