编辑
- 现在可以选择以 16 位浮点数存储。
- 你会失去一些精度（取决于数据范围，改变 rnd 分布以查看不同的错误率）。
- 较慢（20-30 毫秒）（如果重要，请参阅下面的链接了解可能更快的技巧）
- 2mb
- 如果您知道数据的性质（范围、分布表面（可能是可变长度编码）），可能还可以做更多
代码
//using code lifted from http://www.mathworks.com/matlabcentral/fileexchange/23173
#include "opencv2/opencv.hpp"
#include <string.h>
#include <math.h>
using namespace cv;
#define INT16_TYPE short
#define UINT16_TYPE unsigned short
#define INT32_TYPE long
#define UINT32_TYPE unsigned long
int doubles2halfp(void *target, void *source, int numel);
int halfp2doubles(void *target, void *source, int numel);
void writemat(char* fpath,Mat& data,bool isf16)
{
FILE* fp = fopen(fpath,"wb");
if (!fp)perror("fopen");
double dbuf[1024];
for(int i=0;i<1024;++i)
{
for(int j=0;j<1024;++j)
dbuf[j]=data.at<double>(i,j);
if(isf16)
{
UINT16_TYPE hbuf[1024];
doubles2halfp(&hbuf,&dbuf,1024);
fwrite(&hbuf,sizeof(UINT16_TYPE),1024,fp);
}else
{
fwrite(&dbuf,sizeof(double),1024,fp);
}
}
fclose(fp);
}
void readmat(char* fpath,Mat& data,bool isf16)
{
FILE* fp = fopen(fpath,"rb");
if (!fp)perror("fopen");
double dbuf[1024];
for(int i=0;i<1024;++i)
{
if(isf16)
{
UINT16_TYPE hbuf[1024];
fread(&hbuf,sizeof(UINT16_TYPE),1024,fp);
halfp2doubles(&dbuf,&hbuf,1024);
}else{
fread(&dbuf,sizeof(double),1024,fp);
}
for(int j=0;j<1024;++j)
{
data.at<double>(i,j)=dbuf[j];
}
}
fclose(fp);
}
int main()
{
RNG rng= theRNG();
Mat data = Mat::zeros(Size(1024,1024),CV_64FC1);
for(int i=0;i<1024;++i)
for(int j=0;j<1024;++j)
data.at<double>(i,j)=rng.uniform(-1.,1.);
writemat("img.bin",data,true);
Mat res = Mat::zeros(Size(1024,1024),CV_64FC1);
readmat("img.bin",res,true);
double error=0;
for(int i=0;i<1024;++i)
for(int j=0;j<1024;++j)
{
//printf("%f %f\n",data.at<double>(i,j),res.at<double>(i,j));
error+=abs(data.at<double>(i,j)-res.at<double>(i,j));
}
printf("err=%f avgerr=%f\n",error,error/1024/1024);
getchar();
return 0;
}
////////////////////////////////////////
////////////////////////////////////////
////////////////////////////////////////
////////////////////////////////////////
int doubles2halfp(void *target, void *source, int numel)
{
UINT16_TYPE *hp = (UINT16_TYPE *) target; // Type pun output as an unsigned 16-bit int
UINT32_TYPE *xp = (UINT32_TYPE *) source; // Type pun input as an unsigned 32-bit int
UINT16_TYPE hs, he, hm;
UINT32_TYPE x, xs, xe, xm;
int hes;
static int next; // Little Endian adjustment
static int checkieee = 1; // Flag to check for IEEE754, Endian, and word size
double one = 1.0; // Used for checking IEEE754 floating point format
UINT32_TYPE *ip; // Used for checking IEEE754 floating point format
if( checkieee ) { // 1st call, so check for IEEE754, Endian, and word size
ip = (UINT32_TYPE *) &one;
if( *ip ) { // If Big Endian, then no adjustment
next = 0;
} else { // If Little Endian, then adjustment will be necessary
next = 1;
ip++;
}
if( *ip != 0x3FF00000u ) { // Check for exact IEEE 754 bit pattern of 1.0
return 1; // Floating point bit pattern is not IEEE 754
}
if( sizeof(INT16_TYPE) != 2 || sizeof(INT32_TYPE) != 4 ) {
return 1; // short is not 16-bits, or long is not 32-bits.
}
checkieee = 0; // Everything checks out OK
}
xp += next; // Little Endian adjustment if necessary
if( source == NULL || target == NULL ) { // Nothing to convert (e.g., imag part of pure real)
return 0;
}
while( numel-- ) {
x = *xp++; xp++; // The extra xp++ is to skip over the remaining 32 bits of the mantissa
if( (x & 0x7FFFFFFFu) == 0 ) { // Signed zero
*hp++ = (UINT16_TYPE) (x >> 16); // Return the signed zero
} else { // Not zero
xs = x & 0x80000000u; // Pick off sign bit
xe = x & 0x7FF00000u; // Pick off exponent bits
xm = x & 0x000FFFFFu; // Pick off mantissa bits
if( xe == 0 ) { // Denormal will underflow, return a signed zero
*hp++ = (UINT16_TYPE) (xs >> 16);
} else if( xe == 0x7FF00000u ) { // Inf or NaN (all the exponent bits are set)
if( xm == 0 ) { // If mantissa is zero ...
*hp++ = (UINT16_TYPE) ((xs >> 16) | 0x7C00u); // Signed Inf
} else {
*hp++ = (UINT16_TYPE) 0xFE00u; // NaN, only 1st mantissa bit set
}
} else { // Normalized number
hs = (UINT16_TYPE) (xs >> 16); // Sign bit
hes = ((int)(xe >> 20)) - 1023 + 15; // Exponent unbias the double, then bias the halfp
if( hes >= 0x1F ) { // Overflow
*hp++ = (UINT16_TYPE) ((xs >> 16) | 0x7C00u); // Signed Inf
} else if( hes <= 0 ) { // Underflow
if( (10 - hes) > 21 ) { // Mantissa shifted all the way off & no rounding possibility
hm = (UINT16_TYPE) 0u; // Set mantissa to zero
} else {
xm |= 0x00100000u; // Add the hidden leading bit
hm = (UINT16_TYPE) (xm >> (11 - hes)); // Mantissa
if( (xm >> (10 - hes)) & 0x00000001u ) // Check for rounding
hm += (UINT16_TYPE) 1u; // Round, might overflow into exp bit, but this is OK
}
*hp++ = (hs | hm); // Combine sign bit and mantissa bits, biased exponent is zero
} else {
he = (UINT16_TYPE) (hes << 10); // Exponent
hm = (UINT16_TYPE) (xm >> 10); // Mantissa
if( xm & 0x00000200u ) // Check for rounding
*hp++ = (hs | he | hm) + (UINT16_TYPE) 1u; // Round, might overflow to inf, this is OK
else
*hp++ = (hs | he | hm); // No rounding
}
}
}
}
return 0;
}
int halfp2doubles(void *target, void *source, int numel)
{
UINT16_TYPE *hp = (UINT16_TYPE *) source; // Type pun input as an unsigned 16-bit int
UINT32_TYPE *xp = (UINT32_TYPE *) target; // Type pun output as an unsigned 32-bit int
UINT16_TYPE h, hs, he, hm;
UINT32_TYPE xs, xe, xm;
INT32_TYPE xes;
int e;
static int next; // Little Endian adjustment
static int checkieee = 1; // Flag to check for IEEE754, Endian, and word size
double one = 1.0; // Used for checking IEEE754 floating point format
UINT32_TYPE *ip; // Used for checking IEEE754 floating point format
if( checkieee ) { // 1st call, so check for IEEE754, Endian, and word size
ip = (UINT32_TYPE *) &one;
if( *ip ) { // If Big Endian, then no adjustment
next = 0;
} else { // If Little Endian, then adjustment will be necessary
next = 1;
ip++;
}
if( *ip != 0x3FF00000u ) { // Check for exact IEEE 754 bit pattern of 1.0
return 1; // Floating point bit pattern is not IEEE 754
}
if( sizeof(INT16_TYPE) != 2 || sizeof(INT32_TYPE) != 4 ) {
return 1; // short is not 16-bits, or long is not 32-bits.
}
checkieee = 0; // Everything checks out OK
}
xp += next; // Little Endian adjustment if necessary
if( source == NULL || target == NULL ) // Nothing to convert (e.g., imag part of pure real)
return 0;
while( numel-- ) {
h = *hp++;
if( (h & 0x7FFFu) == 0 ) { // Signed zero
*xp++ = ((UINT32_TYPE) h) << 16; // Return the signed zero
} else { // Not zero
hs = h & 0x8000u; // Pick off sign bit
he = h & 0x7C00u; // Pick off exponent bits
hm = h & 0x03FFu; // Pick off mantissa bits
if( he == 0 ) { // Denormal will convert to normalized
e = -1; // The following loop figures out how much extra to adjust the exponent
do {
e++;
hm <<= 1;
} while( (hm & 0x0400u) == 0 ); // Shift until leading bit overflows into exponent bit
xs = ((UINT32_TYPE) hs) << 16; // Sign bit
xes = ((INT32_TYPE) (he >> 10)) - 15 + 1023 - e; // Exponent unbias the halfp, then bias the double
xe = (UINT32_TYPE) (xes << 20); // Exponent
xm = ((UINT32_TYPE) (hm & 0x03FFu)) << 10; // Mantissa
*xp++ = (xs | xe | xm); // Combine sign bit, exponent bits, and mantissa bits
} else if( he == 0x7C00u ) { // Inf or NaN (all the exponent bits are set)
if( hm == 0 ) { // If mantissa is zero ...
*xp++ = (((UINT32_TYPE) hs) << 16) | ((UINT32_TYPE) 0x7FF00000u); // Signed Inf
} else {
*xp++ = (UINT32_TYPE) 0xFFF80000u; // NaN, only the 1st mantissa bit set
}
} else {
xs = ((UINT32_TYPE) hs) << 16; // Sign bit
xes = ((INT32_TYPE) (he >> 10)) - 15 + 1023; // Exponent unbias the halfp, then bias the double
xe = (UINT32_TYPE) (xes << 20); // Exponent
xm = ((UINT32_TYPE) hm) << 10; // Mantissa
*xp++ = (xs | xe | xm); // Combine sign bit, exponent bits, and mantissa bits
}
}
xp++; // Skip over the remaining 32 bits of the mantissa
}
return 0;
}