There's no way to write floating points to a file from the floating point registers st0 <> st7
For example:
; st(0) = 0.0
; Direct evalling
eval "st0: {st(0)}"
log $RESULT ; Logs: "st0: {st(0)}"
; Temporary storing the value
mov flt, st(0) ; flt: 0.0
eval "st0: {flt}"
log $RESULT ; Logs: "st0: {flt}"
; Without text in front
log st(0) ; Works fine...
wrt "test.txt", st(0) ; 'error'