65 lines
2.3 KiB
C++
65 lines
2.3 KiB
C++
/**
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******************************************************************************
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* Xenia : Xbox 360 Emulator Research Project *
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******************************************************************************
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* Copyright 2021 Ben Vanik. All rights reserved. *
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* Released under the BSD license - see LICENSE in the root for more details. *
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******************************************************************************
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*
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* @modified Tom Clay, 2026 - Adapted for ReXGlue runtime
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*/
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#include <cmath>
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#include <rex/ui/graphics_util.h>
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namespace rex {
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namespace ui {
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int32_t FloatToD3D11Fixed16p8(float f32) {
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// https://microsoft.github.io/DirectX-Specs/d3d/archive/D3D11_3_FunctionalSpec.htm#3.2.4.1%20FLOAT%20-%3E%20Fixed%20Point%20Integer
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// Early exit tests.
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// n == NaN || n.unbiasedExponent < -f-1 -> 0 . 0
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if (!(std::abs(f32) >= 1.0f / 512.0f)) {
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return 0;
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}
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// n >= (2^(i-1)-2^-f) -> 2^(i-1)-1 . 2^f-1
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if (f32 >= 32768.0f - 1.0f / 256.0f) {
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return (1 << 23) - 1;
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}
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// n <= -2^(i-1) -> -2^(i-1) . 0
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if (f32 <= -32768.0f) {
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return -32768 * 256;
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}
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uint32_t f32_bits = *reinterpret_cast<const uint32_t*>(&f32);
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// Copy float32 mantissa bits [22:0] into corresponding bits [22:0] of a
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// result buffer that has at least 24 bits total storage (before reaching
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// rounding step further below). This includes one bit for the hidden 1.
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// Set bit [23] (float32 hidden bit).
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// Clear bits [31:24].
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union {
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int32_t s;
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uint32_t u;
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} result;
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result.u = (f32_bits & ((1 << 23) - 1)) | (1 << 23);
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// If the sign bit is set in the float32 number (negative), then take the 2's
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// component of the entire set of bits.
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if ((f32_bits >> 31) != 0) {
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result.s = -result.s;
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}
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// Final calculation: extraBits = (mantissa - f) - n.unbiasedExponent
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// (guaranteed to be >= 0).
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int32_t exponent = int32_t((f32_bits >> 23) & 255) - 127;
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uint32_t extra_bits = uint32_t(15 - exponent);
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if (extra_bits) {
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// Round the 32-bit value to a decimal that is extraBits to the left of
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// the LSB end, using nearest-even.
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result.u += (1 << (extra_bits - 1)) - 1 + ((result.u >> extra_bits) & 1);
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// Shift right by extraBits (sign extending).
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result.s >>= extra_bits;
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}
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return result.s;
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}
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} // namespace ui
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} // namespace rex
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