To give more context to what I asked in the title: I’m using VS C++, and I need to read an 80-bit floating point number from memory and format it into a human-readable form. I can somewhat do it for the Intel x64/x86 architecture, but I’m struggling to figure out how to do it for Aarch64.
PS. For x64, I was able to do it in assembly by converting the 80-bit long double to double using this function:
; RCX = points to `long double` to convert from
; RDX = points to `double` to convert to
FLD tbyte ptr [RCX]
FSTP qword ptr [RDX]
ret
And then by printing the converted double value. It loses some precision, but that’s OK.
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I need to read an 80-bit floating point number from memory and format it into a human-readable form. I can somewhat do it for the Intel x64/x86 architecture, but I’m struggling to figure out how to do it for Aarch64.
Try SoftFloat library, it has floatx80_to_float32, floatx80_to_float64 and floatx80_to_float128. Detect the native format, act accordingly.
#include "softfloat.h"
#include <stdio.h>
#include <stdlib.h>
typedef struct {
void* (*processFloatx80)(floatx80 fx80);
} FloatProcessor;
void* processFloatx80_to_float64(floatx80 fx80) {
float64_t* result = (float64_t*)malloc(sizeof(float64_t));
if (result != NULL) {
*result = floatx80_to_float64(fx80);
}
return result;
}
void* processFloatx80_to_float32(floatx80 fx80) {
float32_t* result = (float32_t*)malloc(sizeof(float32_t));
if (result != NULL) {
*result = floatx80_to_float32(fx80);
}
return result;
}
void* processFloatx80_to_float128(floatx80 fx80) {
float128_t* result = (float128_t*)malloc(sizeof(float128_t));
if (result != NULL) {
*result = floatx80_to_float128(fx80);
}
return result;
}
int main() {
...
floatx80 fx80;
FloatProcessor processor;
#if defined(__FLOAT128__)
processor.processFloatx80 = processFloatx80_to_float128;
#elif defined(__aarch64__) || defined(__arm__) || defined(__x86_64__)
processor.processFloatx80 = processFloatx80_to_float64;
#else
processor.processFloatx80 = processFloatx80_to_float32;
#endif
...
}
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