RuntimeWarning: overflow encountered in scalar subtract

[aghaeifar]

In the following method (file map_twix.py):

def par_offset(self):
    offset = 0
    if self.hdr is not None and self.flags['zf_missing_lines'] and self.base_size['Par']//2 > self.kspace_center_lin + 1:
        offset = self.base_size['Par'] - 2 * self.kspace_center_par
    return offset

The values in the dictionary self.base_size are of type uint16. When performing operations with int32 variables, an overflow can occur.

For example, in the method par_offset, I encountered the following case when reconstructing an mprage data:

• self.base_size['Par'] was 255.
• self.kspace_center_par was 128.

The subtraction result should be -1; however, due to self.base_size['Par'] being uint16, the result is interpreted as 65535 (=2^16 - 1). Consequently, I observed the following runtime warning:

twixtools/map_twix.py:377: RuntimeWarning: overflow encountered in scalar subtract
  offset = self.base_size['Par'] - 2 * self.kspace_center_par

Proposed Solution

To avoid such overflows, I suggest changing the type of self.base_size values from uint16 to int16. This modification ensures that subtraction results are correctly interpreted as negative when applicable.