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Remove conditional fixed point number inlining

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Caused issues with ODR rule violations. Now fixed point numbers should
only be used in ARM-mode. Attempting to use them in Thumb-mode will
cause a compilation failure. This commit also moves operator/ into IWRAM
on the GBA.
This commit is contained in:
Madeline Busig 2024-07-30 11:45:08 -06:00
parent 62da9d03c1
commit 2181557d9d
2 changed files with 93 additions and 74 deletions
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108
include/mtl/fixed.hpp
View File

@ -5,6 +5,8 @@
#include "mtl/target.hpp" #include "mtl/target.hpp"
TARGET_ARM_MODE
namespace mtl { namespace mtl {
/** /**
* \brief 32-bit Fixed point number * \brief 32-bit Fixed point number
@ -19,14 +21,16 @@ namespace mtl {
* *
* \par ARM * \par ARM
* *
* All member functions are compiled in ARM mode because some operators (notably * All functions are compiled in ARM mode because some operators (notably
* multiplication and division) use ARM-only instructions. For optimal performance, * multiplication and division) use ARM-only instructions. For compatability
* fixed point numbers should be used in ARM-mode code to enable inlining. To ensure * and optimal performance, fixed point numbers should only be used in ARM-mode
* inlining is enabled, enclose the include directive in `TARGET_ARM_MODE` and * code. If `operator*` is used in Thumb code, compilation will fail.
* `TARGET_END_MODE` from `<mtl/target.hpp>`. This is necessary because inline assembly * This happens because GCC attempts to inline the function even though it
* is used and GCC can't tell that ARM-only instructions are used, so it tries * cannot be inlined in Thumb-mode. Conditional inlining using TARGET_*_MODE
* to inline in Thumb mode too. If these directives are not used, some operations * is not used because it is fragile, for example, when including into `<vec4.hpp>`
* will not be inlined even in arm mode (ex. multiplication and division). * and also in `foo.cpp`. In this case, `vec4` would attempt to include the
* inlined version but `foo` would not, causing a ODR violation. All other
* operations are usable from Thumb-mode, with a significant performance penalty.
*/ */
class fixed { class fixed {
private: private:
@ -46,10 +50,10 @@ private:
* DO NOT use to set the fixed number to an integer value, use * DO NOT use to set the fixed number to an integer value, use
* the public constructor instead. * the public constructor instead.
*/ */
ARM_MODE constexpr fixed(int32_t _x, bool) : x(_x) {} constexpr fixed(int32_t _x, bool) : x(_x) {}
public: public:
ARM_MODE constexpr fixed() : x(0) {} constexpr fixed() : x(0) {}
/** /**
* \brief Integer constructor * \brief Integer constructor
* *
@ -58,7 +62,7 @@ public:
* the class description for more detail. * the class description for more detail.
*/ */
template <typename T, std::enable_if_t<std::is_integral_v<T>, bool> = true> template <typename T, std::enable_if_t<std::is_integral_v<T>, bool> = true>
ARM_MODE constexpr fixed(T _i) : x(_i * 64) {} constexpr fixed(T _i) : x(_i * 64) {}
/** /**
* \brief Floating point constructor * \brief Floating point constructor
* *
@ -71,7 +75,7 @@ public:
* float. * float.
*/ */
template <typename T, std::enable_if_t<std::is_floating_point_v<T>, bool> = true> template <typename T, std::enable_if_t<std::is_floating_point_v<T>, bool> = true>
ARM_MODE constexpr fixed(T _f) constexpr fixed(T _f)
// 0.5 offset accounts for truncating to integer, round instead // 0.5 offset accounts for truncating to integer, round instead
: x((_f * 64) + 0.5f) {} : x((_f * 64) + 0.5f) {}
@ -84,7 +88,7 @@ public:
* *
* Should not be used unless absolutely needed. * Should not be used unless absolutely needed.
*/ */
ARM_MODE static constexpr fixed from_raw(int32_t x) { static constexpr fixed from_raw(int32_t x) {
return fixed(x, true); return fixed(x, true);
} }
@ -94,7 +98,7 @@ public:
* Gets the raw value of the fixed point number. i.e. The fixed point * Gets the raw value of the fixed point number. i.e. The fixed point
* number multiplied by 64. * number multiplied by 64.
*/ */
ARM_MODE constexpr int32_t raw() const { constexpr int32_t raw() const {
return x; return x;
} }
@ -104,13 +108,13 @@ public:
* Addition with fixed point numbers is the same as with a 32-bit * Addition with fixed point numbers is the same as with a 32-bit
* integer, so should be extremely quick. * integer, so should be extremely quick.
*/ */
ARM_MODE constexpr fixed operator+(fixed rhs) const { constexpr fixed operator+(fixed rhs) const {
return from_raw(x + rhs.x); return from_raw(x + rhs.x);
} }
/** /**
* \brief Fixed point subtraction * \brief Fixed point subtraction
*/ */
ARM_MODE constexpr fixed operator-(fixed rhs) const { constexpr fixed operator-(fixed rhs) const {
return from_raw(x - rhs.x); return from_raw(x - rhs.x);
} }
@ -118,13 +122,13 @@ public:
* \brief Fixed point multiplication * \brief Fixed point multiplication
* *
* Uses an assembly implementation to multiply the two numbers. * Uses an assembly implementation to multiply the two numbers.
*
* \par ARM
*
* Use in ARM-mode only. Attempted use in Thumb-mode will cause a
* compilation failure.
*/ */
#ifdef __ARM_32BIT_STATE // Safe to inline in ARM mode, but not in Thumb mode fixed operator*(fixed rhs) const {
ALWAYS_INLINE // because ARM-mode instructions are used. GCC isn't smart
#else // enough to figure it out on its own
NOINLINE
#endif
ARM_MODE fixed operator*(fixed rhs) const {
int32_t raw_result; int32_t raw_result;
asm( asm(
"smull r8, r9, %[a], %[b];" "smull r8, r9, %[a], %[b];"
@ -149,59 +153,15 @@ public:
* that if a denominator slowly approaches zero, once it reaches zero * that if a denominator slowly approaches zero, once it reaches zero
* the quotient's sign will flip. The largest value is used because fixed * the quotient's sign will flip. The largest value is used because fixed
* point numbers don't have a representation of infinity. * point numbers don't have a representation of infinity.
*
* \par GBA
*
* Placed in IWRAM
*/ */
#ifdef __ARM_32BIT_STATE // Safe to inline in ARM mode, but not in Thumb mode fixed operator/(fixed rhs) const;
ALWAYS_INLINE // because ARM-mode instructions are used. GCC isn't smart
#else // enough to figure it out on its own
NOINLINE
#endif
ARM_MODE fixed operator/(fixed rhs) const {
int32_t raw_result;
asm(
// This division implementation has two methods it can use.
// The fastest uses a left shift followed by a single division. The value is shifted
// first to preserve the decimal part. Unfortunately, this means large numerators
// will cause the operation to overflow. In this case, a compatible method will be
// used. This method uses two divisions, one to calculate the integral quotient,
// and one to calculate the decimal part. Both these methods work for negative numbers as well.
"movs r1, %[d];" // Load numerator and denominator, and check if negative or zero
"beq 4f;"
"movs r0, %[n];"
"blt 1f;"
"tst r0, #0x7e000000;" // Check if the numerator is large enough to overflow
"bne 3f;"
"b 2f;"
"1:" // check_negative
"mvn r2, r0;" // Check if the numerator is large enough to overflow.
"tst r2, #0x7e000000;"
"bne 3f;"
"2:" // fast_div // Fast method
"lsl r0, #6;" // Shift first to avoid truncation
"swi #0x60000;" // GBA Div syscall
"mov %[res], r0;"
"b 5f;"
"3:" // compat_div // Compatible method
"swi #0x60000;" // Compute quotient and shift
"lsl r2, r0, #6;"
"mov r0, r1;" // Div syscall puts the modulus in r1, use it as the numerator
"lsr r1, %[d], #6;" // Load the denominator again, shifted right to calculate decimal part
"swi #0x60000;"
"mov %[res], r2;" // Calculate the final result
"add %[res], r0;"
"b 5f;"
"4:" // zero_div
"teq %[n], %[d];" // Set result to largest possible negative/positive value.
"movmi %[res], #0x80000000;"
"movpl %[res], #0x7FFFFFFF;"
"5:"
: [res] "=r" (raw_result)
: [n] "r" (x),
[d] "r" (rhs.x)
: "r0", "r1", "r2", "r3"
);
return from_raw(raw_result);
}
}; };
} // namespace mtl } // namespace mtl
TARGET_END_MODE

59
src/gba/fixed.cpp Normal file
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@ -0,0 +1,59 @@
#include "mtl/target.hpp"
#include "mtl/fixed.hpp"
TARGET_ARM_MODE
namespace mtl {
GBA_IWRAM fixed fixed::operator/(fixed rhs) const {
int32_t raw_result;
asm(
// This division implementation has two methods it can use.
// The fastest uses a left shift followed by a single division. The value is shifted
// first to preserve the decimal part. Unfortunately, this means large numerators
// will cause the operation to overflow. In this case, a compatible method will be
// used. This method uses two divisions, one to calculate the integral quotient,
// and one to calculate the decimal part. Both these methods work for negative numbers as well.
"movs r1, %[d];" // Load numerator and denominator, and check if negative or zero
"beq 4f;"
"movs r0, %[n];"
"blt 1f;"
"tst r0, #0x7e000000;" // Check if the numerator is large enough to overflow
"bne 3f;"
"b 2f;"
"1:" // check_negative
"mvn r2, r0;" // Check if the numerator is large enough to overflow.
"tst r2, #0x7e000000;"
"bne 3f;"
"2:" // fast_div // Fast method
"lsl r0, #6;" // Shift first to avoid truncation
"swi #0x60000;" // GBA Div syscall
"mov %[res], r0;"
"b 5f;"
"3:" // compat_div // Compatible method
"swi #0x60000;" // Compute quotient and shift
"lsl r2, r0, #6;"
"mov r0, r1;" // Div syscall puts the modulus in r1, use it as the numerator
"lsr r1, %[d], #6;" // Load the denominator again, shifted right to calculate decimal part
"swi #0x60000;"
"mov %[res], r2;" // Calculate the final result
"add %[res], r0;"
"b 5f;"
"4:" // zero_div
"teq %[n], %[d];" // Set result to largest possible negative/positive value.
"movmi %[res], #0x80000000;"
"movpl %[res], #0x7FFFFFFF;"
"5:"
: [res] "=r" (raw_result)
: [n] "r" (x),
[d] "r" (rhs.x)
: "r0", "r1", "r2", "r3"
);
return raw_result;
}
} // namespace mtl
TARGET_END_MODE