Reynolds v. Sims, 377 U.S. 533 (1964) was a United States Supreme Court case that ruled that unlike in the election of the United States Senate, in the election of any chamber of a state legislature the electoral districts must be roughly equal in population (thus negating the traditional function of a State Senate, which was to allow rural counties to counter balance large towns and cities). The case was brought on behalf of voters in Alabama by M.O. Sims, a taxpayer in Birmingham, Alabama, but affected both northern and southern states that had similarly failed to reapportion their legislatures in keeping with changes in state population after its application in five companion cases in Colorado, New York, Maryland, Virginia, and Delaware.

Is it true that the warren court ruled that state legislative districts must be equal in population?
yes