si.cpp

Go to the documentation of this file.

#include "roo_quantity/si.h"
 
#include <cmath>
#include <cstdio>
 
namespace roo_quantity {
 
void FormatSimpleSiValue(float val, const char* base_unit, char* out,
                         int maxlen) {
  if (isnanf(val)) {
    snprintf(out, maxlen, "? %s", base_unit);
    return;
  }
  if (val == 0.0f) {
    snprintf(out, maxlen, "0 %s", base_unit);
    return;
  }
  const char* prefix;
  const char* sign = "";
  if (val < 0.0f) {
    sign = "-";
    val = -val;
  }
  if (std::isinf(val)) {
    snprintf(out, maxlen, "%s∞ %s", sign, base_unit);
    return;
  }
  if (val >= 1000000000000000.0f) {
    prefix = "P";
    val *= 0.000000000000001;
  } else if (val >= 1000000000000.0f) {
    prefix = "T";
    val *= 0.000000000001;
  } else if (val >= 1000000000.0f) {
    prefix = "G";
    val *= 0.000000001;
  } else if (val >= 1000000.0f) {
    prefix = "M";
    val *= 0.000001;
  } else if (val >= 1000.0f) {
    prefix = "k";
    val *= 0.001;
  } else if (val >= 1.0f) {
    prefix = "";
  } else if (val >= 0.001f) {
    prefix = "m";
    val *= 1000.0f;
  } else if (val >= 0.000001f) {
    prefix = "µ";
    val *= 1000000.0f;
  } else if (val >= 0.000000001f) {
    prefix = "n";
    val *= 1000000000.0f;
  } else {
    prefix = "p";
    val *= 1000000000000.0f;
  }
  snprintf(out, maxlen, "%s%g %s%s", sign, val, prefix, base_unit);
}
 
}  // namespace roo_quantity